Study Notes Exam 5
Body Fluid Regulation
- Water and Ion Balance
o the excretory system regulates body fluid concentrations by regulating the water and mineral ions (i.e., Na+, CI-, K+, and HCO3-) in body fluids
o water enters animals when they eat foods and drink water, and by metabolism where cellular respiration produces water
o water is lost by evaporation from skin and lungs, through feces, and by excretion
o to be in balance, the water entering the body must equal the water lost
o if osmolarity differs between two regions, water moves into the region with the higher amount of solutes
o marine environments are high in salt and promote the loss of water and the gain of ions by drinking water
o freshwater promotes water gain by osmosis & ion loss as excess water is excreted
o terrestrial animals tend to lose both water and ions to the environment
- Aquatic Animals
o Cartilage Fishes and Marine Invertebrates: sharks and rays are nearly isotonic with seawater; yet they do not contain the same amount of salt as seawater
§ their blood has high concentrations of urea to match the tonicity of seawater; for some reason this is not toxic to them
o Marine Bony Fishes constantly drink seawater; they are prone to water loss and could become dehydrated
§ to remove excess salt, they actively export Na+ and Cl- ions at the gills
§ bony fishes have a moderate salt level compared to seawater, their common ancestor probably evolved in freshwater
o Freshwater Bony Fishes never drink water; they passively gain water which makes their body fluids hypertonic to freshwater
§ they take in salts at the gills and pass large quantities of hypotonic urine
§ because this causes them to lose salts, they actively import Na+ and Cl- ions into the blood at the gills
§ some fish can move between marine and freshwater environments (salmon begin life in freshwater streams, mature in oceans and breed in freshwater)
- Terrestrial Animals: some terrestrial animals near oceans are able to drink seawater despite its high osmolarity - such birds and reptiles have a nasal salt gland that excretes concentrated salt solution
o Water Loss Prevention: some animals excrete insoluble nitrogenous waste
§ animal skin is adapted to moist (thin, permeable skin) or dry (thick, impermeable skin) environments
§ some animals have other unique adaptations to prevent water loss (the camel and kangaroo rat absorb moisture from exhaled air)
o Most terrestrial animals must drink fresh water often; however, the kangaroo rat completely avoids drinking water (metabolic water is enough; forms concentrated urine & dry fecal waste)
Nitrogenous Waste Products
- Eliminating Nitrogenous Wastes: the breakdown of nucleic acids and amino acids results in nitrogenous wastes
o amino acids are used to synthesize body proteins; unused amino acids are oxidized to generate energy or are stored as fats or carbohydrates
o in both cases, amino groups (—NH2) must be removed
o nitrogenous waste is excreted as ammonia, urea, or uric acid - depends on animal
- Excreting Ammonia: bony fishes, aquatic invertebrates, and amphibians excrete ammonia through gills and skin surfaces
o amino groups removed from amino acids form ammonia (NH3) by adding a third hydrogen ion (H+); this requires little or no energy
o ammonia is quite toxic but is water soluble; it requires much water to wash away
- Excreting Urea: terrestrial amphibians and mammals usually excrete urea as their main nitrogenous waste
o urea is much less toxic than ammonia; excreted in a moderately concentrated solution, it also conserves body water
o urea is produced in the liver as a product of the energy-requiring urea cycle
- Excreting Uric Acid: insects, reptiles, and birds excrete uric acid as their main nitrogenous waste
o uric acid is not very toxic and is poorly soluble in water; uric acid is readily concentrated for water conservation
o in reptiles and birds, a dilute uric acid passes from the kidneys to the cloaca, a common reservoir for products of the digestive, urinary, and reproductive systems
o after any water is absorbed by the cloaca, the uric acid passes out with the feces
o eggshells with reptile and bird embryos store uric acid that builds up (nontoxic)
o uric acid synthesis by enzymatic reactions uses more ATP than urea synthesis
o therefore, there is a trade-off between water conservation and energy expenditure
Organs of Excretion: most animals have tubular organs to regulate salt-water balance and excrete metabolic wastes
- flame cells in planarians are ciliated cells along excretory tubules that open to the outside through excretory pores
o flickering cilia propel a hypotonic fluid through canals emptying at body surface
o system functions in excess water excretion, osmotic regulation, & waste excretion
- nephridia in earthworms are paired tubules in each segment with a ciliated opening, the nephridiostome, and an excretory nephridiopore
o fluid from the body cavity is filtered through this tubule by cilia
o the nephridia form urine that contains only metabolic wastes, salts, and water
o an earthworm produces enough water that it can safely excrete ammonia
- Malpighian tubules in insects guts take up metabolic wastes and water from hemolymph; these follow salt gradient established by active transport of K+ ions
o at the rectum, water and other useful substances are reabsorbed
o uric acid remains and eventually passes out the anus
Urinary System in Humans: the human urinary system has four parts:
- the human kidneys are two bean-shaped, reddish brown organs about the size of a fist
- they are located laterally in the abdominopelvic cavity (retroperitoneal)
o the kidneys are the sites of urine formation
o each kidney is connected to a ureter conducting urine to the urinary bladder
o urinary bladder stores urine until it is voided from the body through urethra
o male urethra runs through penis and conducts semen; in females, it opens ventral to vaginal opening
- Kidneys: a longitudinal section distinguishes three major regions
o the renal cortex is the thin, outer region of a kidney and it appears granular
o the renal medulla consists of the striped, pyramid-shaped regions that lie on the inner side of the cortex
o the renal pelvis is the innermost hollow chamber of the kidney
o each human kidney is composed of about one million tiny tubules called nephrons (primarily in cortex but some dip down into the medulla)
- Nephrons: each nephron is comprised of several parts:
o the end of a nephron forms a cuplike structure called the glomerular capsule (2 layers: outer simple squamous epithelium; inner podocytes for filtration)
o nearest the glomerular capsule is the proximal convoluted tubule lined by cells with many mitochondria and tightly packed microvilli
o simple squamous epithelium forms the loop of Henle, the middle portion of the nephron tubule with a descending and ascending limb
o the distal convoluted tubule is the distal portion of the nephron tubule; several join to deliver the urine into collecting ducts
o the loop of nephron and the collecting duct give pyramids of the medulla their striped appearance
o pathway of blood through kidney: aorta®renal artery & branches®afferent arteriole®glomerulus (capillary bed)®efferent arteriole®peritubular capillaries®venous branches & renal vein®inferior vena cava
- Urine Formation requires three distinct processes: glomerular filtration, tubular reabsorption and tubular secretion
- Glomerular Filtration
o when blood enters the glomerulus, blood pressure moves small molecules from the glomerulus across inner capsule to capsular space (pressure filtration)
o the glomerular walls are 100 times more permeable than most capillaries
o filtrate: molecules that leave the blood and enter the glomerular capsules
o plasma proteins and blood cells are too large to be part of the glomerular filtrate
o failure to restore fluids would soon cause death from loss of water, nutrients, and low blood pressure
- Tubular Reabsorption of fluids from the nephron back to the blood occurs through the walls of the proximal convoluted tubule
o reabsorption recovers much of the glomerular filtrate
o the osmolarity of the blood equals the filtrate so osmosis of water does not occur
o sodium ions are actively reabsorbed, pulling along chlorine
o this changes the osmolarity of the blood so that water moves passively from the tubule back to the blood
o about 60–70% of salt and water are reabsorbed at the proximal convoluted tubule
o only molecules with carrier molecules are reabsorbed (e.g.: if there is more glucose than carriers, excess glucose will appear in the urine)
o in diabetes mellitus, there is a too much glucose because the liver fails to store glucose as glycogen
- Tubular Secretion moves substances from the blood to the tubular lumen by other than glomerular filtration
o secretion back into the filtrate primarily occurs at the distal convoluted tubule
o this helps rid the body of potentially harmful compounds that didn¹t enter filtrate
o uric acid, hydrogen ions, ammonia, and penicillin are eliminated this way
- Maintaining the Water-Salt Balance
o salt (NaCl) passively diffuses out of the lower ascending limb of the loop; the upper ascending limb actively transports salt into the renal medulla
o the ascending limb transports less salt & is impermeable to water
o water leaves descending limb of loop along its length to balance salt output
o urea leaks from the lower portion of the collecting ducts
o fluid in the collecting duct is isotonic to cells of cortex; but water diffuses out of the collecting duct into the renal medulla
o the urine finally delivered to the renal pelvis is usually hypertonic to blood plasma
o antidiuretic hormone (ADH) released from the posterior pituitary acts on the collecting ducts by increasing permeability to H2O, increasing H2O retention
§ when ADH is released, more water is reabsorbed and there is less urine
§ during dehydration, the hypothalamus releases ADH (antidiuresis = less urine)
o reabsorption of salt: usually > 99% of sodium in filtrate is reabsorbed by blood
§ most is reabsorbed by proximal tubule (some salt also reabsorbed by ascending limb, distal tubule & collecting duct)
o aldosterone is a hormone secreted by the adrenal cortex that acts on the distal convoluted tubules to increase the reabsorption of Na+ and excretion of K+
§ increased Na + in the blood causes water to be reabsorbed, increasing blood volume and pressure
§ aldosterone secretion is triggered by renin-angiotensin-aldosterone system
§ angiotensin II is a vasoconstrictor (increases blood pressure) & stimulates cells in the adrenal cortex to produce aldosterone
o atrial natriuretic hormone (ANH) is produced when heart atria stretch
§ when blood pressure rises, the heart produces ANH to inhibit the secretion of renin and the release of ADH to decrease blood volume and pressure
- Maintaining the Acid-Base Balance
o the bicarbonate buffer system and breathing work together to maintain blood pH
o excretion of H+ and NH3, and reabsorption of bicarbonate (HCO3-) is adjusted
§ if the blood is basic, fewer hydrogen ions are excreted and fewer sodium and bicarbonate ions are reabsorbed (CO2 + H2O « H2CO3 « H+ + HCO3-)
§ if the blood is acidic, H+ ions are excreted with ammonia, while Na+ and HCO3- ions are reabsorbed
§ ammonia is produced in the tubule cells by deamination of amino acids
o reabsorption or excretion of ions by the kidneys is a homeostatic function that maintains the pH of the blood and osmolarity
Chapter 39: Neurons and Nervous Systems
Evolution of the Nervous System
- Invertebrate Nervous Organization
o even primitive cellular sponges respond by closing the osculum
o hydra (cnidarians) possess a nerve net that allows them to contract, extend, and move tentacles to move & capture prey
o complex cnidaria (sea anemones and jellyfish) may have two nerve nets
o the planarian nervous system is bilaterally symmetrical with two lateral nerve cords that allow rapid transfer of information from anterior to posterior
§ planaria have cephalization with an anterior simple brain composed of a cluster of neurons or ganglia
§ brain receives input from photoreceptors in eyespots & receptors in auricles
§ planarian nervous system parallels central & peripheral system of vertebrates
o annelids, arthropods and molluscs have true nervous systems
§ the nerve cord has a ganglion in each segment to control muscles of segment
§ the brain still receives sensory information and controls the activity of the ganglia so the entire animal is coordinated
- Vertebrate Nervous Organization: vertebrate nervous systems exhibit cephalization and bilateral symmetry
o vertebrate nervous system is composed of central and peripheral nervous systems
§ the central nervous system develops a brain and spinal cord from the embryonic dorsal nerve cord
§ the peripheral nervous system consists of paired cranial and spinal nerves
§ paired eyes, ears, and nasal cavities gather information from environment
§ the vertebrate nervous system may have a thousand to a billion times more neurons than an insect (~ a million neurons in insect)
o The Vertebrate Brain is at the anterior end of the dorsal tubular nerve cord
o the vertebrate brain is customarily divided into the hindbrain, midbrain, and forebrain
§ hindbrain: involuntary control (heart & breathing rate; motor coordination)
§ midbrain & optic lobes: visual reflex center
§ forebrain (cerebrum): receives sensory input from other lobes & regulates conscious output
- The Human Nervous System has three specific functions: receive sensory input, perform integration, and generate motor output to muscles and glands
o the central nervous system (CNS) is located in the midline of the body and integrates sensory information and controls the body
o the peripheral nervous system (PNS) lies outside the CNS and contains the cranial and spinal nerves; it is divided into the somatic and autonomic systems
§ the somatic system controls the skeletal muscles
§ the autonomic system controls smooth muscle, cardiac muscle, and glands
o the CNS and PNS are connected & work together to carry out functions
Nervous Tissue is neurons and neuroglia, which support and nourish neurons
- Neurons vary in size and shape but they all have three parts
o the cell body contains the nucleus and other organelles
o dendrites receive information and conduct impulses toward the cell body
o the axon conducts impulses away from cell body to stimulate or inhibit a neuron, muscle, or gland
- myelination: long axons (nerve fibers) are covered by a white myelin sheath
o the myelin sheath is formed by tightly spiraled neuroglial cells (neurolemmocytes (Schwann cells) in PNS and oligodendrocytes in CNS
o gaps between adjacent neuroglial cells in sheath are called neurofibril nodes
- Types of Neurons
o motor neurons are multipolar & conduct impulses from CNS to muscle & glands
o sensory neurons are unipolar and conduct impulses from periphery toward CNS
o interneurons are multipolar and convey messages between the parts of the CNS
§ they form complex brain pathways for thinking, memory, language, etc.
- Transmission of the Nerve Impulses
o resting membrane potential: -65 mV when an axon is not conducting an impulse; this indicates that the inside of the neuron is more negative than outside
o the sodium-potassium pump maintains an unequal distribution of Na+ (more outside cell) and K+ (more inside cell) ions
o sodium & potassium tend to diffuse across membrane; since the membrane is more permeable to potassium ions than sodium ions, there are more positive ions outside; this accounts for polarity, along with negative proteins inside cell
- Action Potential: rapid change in the membrane potential during impulse conduction
o protein-lined channels in axomembrane open to allow either sodium or potassium ions to pass; these are sodium and potassium gates
o the action potential is generated only after the occurrence of a threshold value
o the potential goes from -65 mV to +40 mV in a depolarization phase
o the potential returns to -65 mV again in the repolarization phase
o at completion, there are more potassium ions outside and more sodium ions inside
- Propagation of Action Potentials
o if an axon is unmyelinated, an action potential stimulates an adjacent axomembrane to produce an action potential
o in myelinated fibers, the action potential at one neurofibril node causes action potential at next node (saltatory conduction; signal jumps from node to node)
o saltatory conduction may reach rates of over 100 meters/second, compared to 1 meter/second without it
o as each impulse passes, the membrane undergoes a short refractory period before it can open the sodium gates again
o the conduction of a nerve impulse is an all-or-nothing event (one-way direction)
- Transmission Across a Synapse
o synapse: small space between axon bulb and cell body of next neuron; it consists of a presynaptic membrane, a synaptic cleft, and the postsynaptic membrane
o synaptic vesicles store neurotransmitters that diffuse across the synapse
§ vesicles fuse with presynaptic memnrane & dump nerotransmitter into synapse; at postsynaptic membrane, neurotransmitters bind with specific receptors
§ neurotransmitter/receptor pair determines if response is excitation/inhibition
- Neurotransmitter Molecules: at least 25 different neurotransmitters identified
o acetylcholine (Ach) and norepinephrine (NE) are common neurotransmitters
o after neurotransmitter initiates a response it is then removed from the cleft
o in some synapses, the postsynaptic membrane contains enzymes that rapidly inactivate the neurotransmitter (acetylcholinesterase breaks down acetylcholine)
o in other synapses, the presynaptic membrane reabsorbs neurotransmitter
o the short existence of neurotransmitters in a synapse prevents continuous stimulation (or inhibition) of postsynaptic membranes
o many drugs that affect the nervous system act by interfering with or stimulating the action of neurotransmitters
- Synaptic Integration
o a neuron has many dendrites and may have 1-10,000 synapses with other neurons
o a neuron receives many excitatory and inhibitory signals - excitatory signals have a depolarizing effect; inhibitory signals have a hyperpolarizing effect
o integration is the summing up of excitatory and inhibitory signals
o if a neuron receives many excitatory signals, or at a rapid rate from one synapse, the axon will probably transmit a nerve impulse
o if both positive and inhibitory signals are received, the summing may prohibit the axon from firing
Central Nervous System: Brain and Spinal Cord
- Introduction to the CNS
o the CNS receives sensory impulses and initiates motor control
o protective coverings
§ cranial bones (brain) & vertebral column (spinal cord)
§ cranial & spinal meninges
§ cerebrospinal fluid (CSF) cushions & protects brain & spinal cord within meninges, cebtral canal of spinal cord & ventricles (cavities) in brain
- The Spinal Cord: the center for many reflex actions and a means of communication between the brain and the spinal nerves
o Gray Matter: butterfly or H-shaped region at center of spinal cord containing unmyelinated cell bodies and short fibers (look gray)
§ contains portions of sensory and motor neurons connected by interneurons
o White Matter: outer regions of spinal cord containing myelinated long fibers of interneurons running together in tracts (look white)
§ tracts conduct impulses between the brain and the spinal nerves; ascending tracts are dorsal and descending tracts from the brain are ventral
§ tracts cross over in brainstem (left side of brain controls right side of body)
- The Brain
o brain has four ventricles: two lateral ventricles and a third and fourth ventricle
o The Cerebrum is the largest part of the brain in humans
§ it receives sensory input and carries out integration to direct motor responses
§ the cerebrum carries out higher thought processes for learning and memory, language and speech
§ corpus callosum: nerve fibers connecting right and left cerebral hemispheres
§ cerebral cortex: outer region; convoluted gray matter containing cell bodies
· contains 4 lobes: the frontal, parietal, occipital, and temporal lobes
· different functions are associated with each lobe
· the cerebral cortex contains motor, sensory, and association areas
· primary motor area: precise control over voluntary movement
· premotor area: organizes motor functions before the primary area sends signals to the cerebellum
· the left frontal lobe has Broca¹s area for our ability to speak
· sensory information from the skin and skeletal muscles arrives at a primary somatosensory area
· primary visual area in the occipital lobe receives information from eyes; a visual association area associates information with old visual information
· primary auditory area in the temporal lobe receives information from ears
· the primary taste area is in the parietal lobe
· somatosensory association area processes and analyzes sensory information from skin and muscles
· general interpretation area receives information from all of the sensory association areas and allows us to quickly integrate signals and send them to the prefrontal area for immediate response
· the prefrontal area in the frontal lobe receives input from other association areas and reasons and plans
§ White Matter in CNS consists of long myelinated axons organized into tracts
· descending tracts from the primary motor area communicate with lower brain centers
· ascending tracts from lower brain centers send sensory information up to the primary somatosensory area
· these tracts cross over near the brain; therefore the left side of the brain controls the right side of the body
§ Basal Nuclei: masses of gray matter located deep within the white matter
· these basal nuclei integrate motor commands; malfunctions cause Huntingdon and Parkinson disease
o The Diencephalon: hypothalamus and thalamu; third ventricle
§ the hypothalamus maintains homeostasis; regulates hunger, sleep, thirst, body temperature, water balance, and blood pressure
· it controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems
§ the thalamus is the last portion of the brain for sensory input before the cerebrum; it is a central relay station for sensory impulses traveling up from the body or from the brain to cerebrum
§ the pineal gland secretes hormone melatonin
o The Cerebellum: 2 lobes separated from brain stem by fourth ventricle
§ integrates impulses from higher centers to coordinate muscle actions, maintain equilibrium and muscle tone, and sustain normal posture
§ assists in the learning of new motor skills, as in sports or playing the piano
o The Brain Stem: the medulla oblongata, pons, and midbrain
§ contains reflex centers for visual, auditory, and tactile responses
§ the pons is a bridge between the cerebellum and rest of CNS
§ the medulla oblongata lies between the spinal cord and the pons
§ it contains vital centers for regulating heartbeat, breathing, and vasoconstriction and reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing
§ it contains nerve tracts that ascend or descend between the spinal cord and the brain¹s higher centers
o The Limbic System blends higher mental functions and primitive emotions
§ the hippocampus makes prefrontal area aware of past experiences stored in association areas
§ the amygdala causes experiences to have emotional overtones
§ inclusion of the frontal lobe in the limbic system allows reasoning to keep us from acting out strong feelings
§ Learning and Memory: memory is the ability to hold thoughts in the mind and to recall past events
· learning takes place when we retain and utilize past memories
· the prefrontal area in the frontal lobe is active in short-term memory (e.g., telephone numbers)
· long-term memory is a mix of semantic memory (numbers, words) and episodic memory (persons, events)
· skill memory is the ability to perform motor activities
· the hippocampus serves as a go-between to bring memories to mind
· the amygdala is responsible for fear conditioning and associates danger with sensory stimuli
· extinction of too many cells in the hippocampus is the underlying cause of Alzheimer disease
Peripheral Nervous System: lies outside the CNS
- Cranial nerves connect to the brain; humans have 12 pairs
- Spinal nerves lie on either side of the spinal cord; humans have 31 pairs
- Ganglia are collections of cell bodies in the PNS
- Cranial nerves mostly connect to the head, neck, and facial regions; the vagus nerve also branches to the pharynx, larynx, and some internal organs
- Somatic System: nerves that carry sensory information to the CNS and motor commands away from the CNS to skeletal muscles
- any voluntary control of muscles involves the brain; reflexes involve the brain or spinal cord
- The Reflex Arc: reflexes are automatic, involuntary responses
- a reflex arc involves the following pathway
o sensory receptors generate an impulse in a sensory neuron that moves along sensory axons toward the spinal cord
o sensory neurons enter the cord dorsally and pass signals to interneurons
o impulses travel along motor axons to an effector, which brings about a response to the stimulus
o some impulses extend to the cerebrum, which makes a person conscious of the stimulus and the reaction
- Autonomic System: regulates cardiac and smooth muscle and glands
o there are two divisions: the sympathetic and parasympathetic systems
o Sympathetic Division: most preganglionic fibers of the sympathetic system arise from the middle (thoracic-lumbar) portion of the spinal cord and almost immediately terminate in ganglia that lie near the cord (thoracic-lumbar portion)
§ the preganglionic fiber is short; the postganglionic fiber is long
§ the sympathetic system is especially important during emergency situations (the ³fight or flight² response)
§ to defend or flee, muscles need a supply of glucose and oxygen; the sympathetic system accelerates heartbeat, and dilates bronchi. 5. To divert energy from less necessary digestive functions, the sympathetic system inhibits digestion
§ the neurotransmitter released by the postganglionic axon is mainly norepinephrine, similar to epinephrine (adrenaline) used as a heart stimulant
o Parasympathetic Division: consists of a few cranial nerves, including the vagus nerve, and fibers that arise from the bottom craniosacral portion of the spinal cord
§ the preganglionic fibers are long and the postganglionic fibers are short
§ this system is a ³housekeeper system²; it promotes internal responses resulting in a relaxed state
§ the parasympathetic system causes the eye pupil to constrict, promotes digestion, and retards heartbeat
§ the neurotransmitter released is acetylcholine
Endocrine System: a system of small glands scattered throughout the body that influences the metabolic activities of cells through hormones
- endocrine glands are ductless glands in contrast to exocrine glands with ducts
- endocrine system consists of endocrine glands that coordinate body activities through hormones; their hormones are secreted directly into bloodstream
- the principal human endocrine glands include:
o the hypothalamus, pineal, and pituitary gland located in the brain
o the thyroid and parathyroid glands located in the neck
o the ovaries located in the abdomen, and the testes in the scrotum
o the thymus located in the thorax
- the endocrine system is especially involved with homeostasis
- protein hormones must be injected because they would be digested if taken orally
- the effect of hormones is controlled by negative feedback and by antagonistic hormone action
o endocrine glands can be sensitive to the condition monitored or to the level of hormone produced
§ several hormones affect the blood glucose, calcium, and sodium levels
§ others are involved in the maturation and function of organs (i.e., gonads, etc.)
o negative feedback control is one mechanism
§ the pancreas produces insulin when blood glucose rises; this causes the liver to store glucose
§ when glucose is stored, the glucose level goes down and the pancreas stops insulin production
o antagonistic actions of hormones can control hormonal regulation
§ the effect of insulin is offset by the production of glucagon by the pancreas
§ thyroid lowers blood calcium level but parathyroids raise blood calcium level
Chemical Signals are used between individuals, between body parts, and between cells
- pheromones are environmental signals that act at a distance between individual organisms
o ants lay down a pheromone trail for other members to find food
o the female silkworm moth releases a pheromone to lure a male moth miles away
- endocrine secretions or hormones are environmental signals that act at a distance between body parts
- hormones are organic chemicals produced by one set of cells that affect a different set
- hormones travel through the entire circulatory system until reaching their target organ
- cells respond to a hormone depending on their receptors
- cells that can react with a hormone have receptor proteins that combine with the hormone in a lock-and-key manner
- this also includes the secretions of neurosecretory cells into the hypothalamus
- some signals act locally between adjacent cells without entering the bloodstream
o neurotransmitters released by neurons belong to this category
o prostaglandins and growth factors are also called local hormones; they affect neighboring cells and do not flow by the bloodstream
o growth factors are local hormones that promote cell division and mitosis.
- axillary secretions of men and women may have some effect on other people; women may synchronize their menstrual cycles with co-workers and some women may prefer the axillary odor of men with a different HLA plasma membrane protein
The Action of Hormones
- peptide hormones are produced from amino acids or proteins
o they cannot enter a cell so they bind to a receptor protein in plasma membrane
o epinephrine is an example that binds to a receptor protein; a relay system leads to conversion of ATP to cyclic AMP
o cyclic AMP (cAMP) is made from ATP; it has one phosphate group attached to adenosine at two locations
o peptide hormones are first messenger; cAMP and calcium are second messengers
o the second messenger sets an enzyme cascade in motion
o activated enzymes can be used repeatedly, resulting in a thousand-fold response.
- steroid hormones are produced from cholesterol; they all have the same complex of 4 carbon rings but different side chains
o steroid hormones are lipids and cross cell membranes freely
o inside the cytoplasm or a nucleus, hormones such as estrogen and progesterone bind to a specific receptor
o the hormone-receptor complex binds to DNA resulting in activation of genes that produce enzymes
Major Endocrine Glands:
Hypothalamus and Pituitary Gland
Hypothalamus: regulates the internal environment through the autonomic system
- it controls heartbeat, temperature, water balance, as well as glandular secretions of the pituitary gland
Pituitary Gland: ~ 1 cm in diameter and lies just below the hypothalamus (connected by stalk-like structure)
- it is comprised of two portions: the posterior pituitary and the anterior pituitary
- Posterior Pituitary: stores & releases 2 hormones (antidiuretic hormone & oxytocin) produced by neurosecretory cells in the hypothalamus and sent through axons to the posterior pituitary
o antidiuretic hormone (ADH or vasopressin) promotes reabsorption of water from the collecting ducts in the kidneys
§ nerve cells in the hypothalamus determine when the blood is too concentrated; ADH is released and the kidneys respond by reabsorbing water
§ as the blood becomes dilute, ADH is no longer released; this is a case of negative feedback
o oxytocin stimulates uterine muscle contraction in response to uterine wall nerve impulses and stimulates the release of milk from mammary glands
§ this positive feedback increases intensity; such positive feedback does not maintain homeostasis
- Anterior Pituitary: stimulation by the hypothalamus controls the release of anterior pituitary hormones through a blood capillary portal system
o the hypothalamus produces & releases hypothalamic-releasing & hypothalamic-inhibiting hormones which pass to the anterior pituitary by this portal system
§ thyroid-releasing hormones released from the hypothalamus act on cells in the anterior pituitary to stimulate production and secretion of a specific hormone
§ thyroid-inhibiting hormones released from the hypothalamus act on cells in the anterior pituitary to inhibit production and secretion of a specific hormone
o the anterior pituitary produces 6 different hormones, each by a distinct cell type
o three of these anterior pituitary hormones affect other glands
o thyroid-stimulating hormone (TSH) stimulates thyroid to produce & secrete thyroxin
o adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to release cortisol (hydrocortisone)
o gonadotropic hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH) act on the gonads (ovaries and testes) to secrete sex hormones
o the other three hormones have direct effects on the body
o prolactin (PRL) is produced in quantity only after childbirth
§ prolactin causes the mammary glands to produce milk
§ it also plays a role in carbohydrate and fat metabolism
o melanocyte-stimulating hormone (MSH) causes skin color changes in fishes, amphibians, and reptiles with melanophores, special skin cells
o growth hormone (GH or somatotropic hormone)
§ GH promotes skeletal and muscular growth
§ GH acts to stimulate the transport of amino acids into cells and to increase the activity of ribosomes
§ GH promotes fat metabolism rather than glucose metabolism
§ too little GH during childhood makes an individual a pituitary dwarf
§ too much forms a giant; life expectancy is less because GH affects blood glucose levels and promotes diabetes mellitus
§ the overproduction of GH in adults results in acromegaly; since long bone growth is no longer possible, only the feet, hands, and face grow
Thyroid Gland: in the neck and attached to the trachea just below the larynx
- thyroid hormone (T3 & T4) are produced in thyroid follicles by combining iodine with tyrosine amino acids
o thyroxine (T4) has 4 iodine atoms; triiodothyronine (T3) has 3 iodine atoms
o thyroid hormones increase the metabolic rate of all organs in the body
o lack of iodine causes enlargement of the thyroid (goiter); easily prevented by supplementing iodine intake in salt
o cretinism results from low thyroid function since birth
§ they are short and stocky and have had hypothyroidism since infancy
§ thyroid treatment helps but unless it is begun in the first two months, mental retardation can occur
o myxedema is hypothyroidism in adults; thyroid hormones can restore normal function
o hyperthyroidism (Graves disease) occurs when thyroid gland is enlarged or overactive
§ exophthalmic goiter: eyes protrude due to edema in the eye socket tissue
§ often cured by removal or destruction of thyroid tissue by surgery or radiation
- calcitonin lowers calcium level in the blood and increases deposits in the bone by reducing osteoclasts
o calcitonin is also necessary for blood clotting
o if blood calcium is lowered to normal, the release of calcitonin is inhibited
o too low calcium levels stimulate the release of parathyroid hormone (PTH).
Parathyroid Glands: paired glands (usually 4) on posterior aspect of thyroid gland
- Parathyroid hormone (Parathormone or PTH): raises blood calcium levels by stimulating osteoclasts, enhancing absorption of calcium by kidneys, & increasing absorption of calcium by cells of intestine
o PTH activates the inactive form of vitamin D in the kidneys; vitamin D enhances absorption of calcium by intestine
o if PTH is not produced in response to low blood Ca2+, tetany (sustained muscle contraction) results because calcium ions play an important role in nerve conduction and muscle contraction
Adrenal Glands (Suprarenal Glands): pyramid-shaped glands above kidneys
- Adrenal Cortex: releases corticosteroid hormones; regulated by ACTH from anterior pituitary
o mineralocorticoids: regulate salt concentrations in extracellular fluids
§ aldosterone: primary mineralocorticoid: enhances sodium (& water) reabsorption from kidney tubules
· sodium ion concentration in body fluids also regulated by renin-angiotensin system, ACTH & atrial natriuretic hormone (ANH)
o glucocorticoids: influence metabolism of body cells & help resist stressors
§ during times of stress (injury/blood loss), glucocorticoids stimulate gluconeogenesis (glucose synthesis) & mobilize fats & proteins to be used for energy to save glucose for the brain
§ cortisol (hydrocortisone) is major glucocorticoid (also cortisone & corticosterone)
§ glucocorticoids also prevent water loss from cells into tissue fluids; used as anti-inflammatory agents
o Addison¹s disease: low level of adrenal cortex hormones resulting in bronzing of skin, low blood sugar (low energy & weak immunity) & low blood sodium (low blood pressure)
o Cushing syndrome: high level of adrenal cortex hormones resulting in high blood sugar (& possibly diabetes mellitus), high blood sodium (hypertension), swelling & obesity & possible masculinization in women
- Adrenal medulla: releases catecholamines (norepinephrine & epinephrine)
o release is stimulated by sympathetic nervous system (³fight or flight² response)
o epinephrine: stimulates heart rate & metabolism
o norepinephrine: influences peripheral vasoconstriction & blood pressure
Pancreas: in the abdomen between the kidneys and near the duodenum
- releases insulin & glucagon from islets of Langerhans
- insulin: released by beta cells of islets; lowers blood glucose levels by stimulating glucose storage & uptake of glucose by cells for energy
o insulin deficiency may leads to diabetes mellitus
§ blood glucose rises due to lack of insulin; kidneys excrete glucose (can use urine test for diabetes)
§ cells can¹t take up glucose for energy & start breaking down fats & proteins for energy, which produces ketones in blood; resulting acidosis & reduced blood volume can lead to coma & death
§ insulin-dependent dibetes mellitus (IDDM): autoimmune disease where immune cells attack & destroy beta cells
§ non-insulin-dependent diabetes mellitus (NIDDM): insulin receptors do not properly respond to insulin
- glucagon: raises blood glucose levels by stimulating glucose removal from glycogen storage deposits in liver cells & gluconeogenesis (new glucose production from lipid & amino acids)
Gonads: produce steroidal sex hormones
- estrogens & progesterone: produced by ovary cells; responsible for maturation of female reproductive organs, uterine cycle & oocyte production
- testosterone: produced by cells of testes; responsible for maturation of male reproductive organs & sperm cell production
o testosterone also affects sex drive, sweat glands, expression of baldness, etc.
o anabolic steroids are supplemental testosterone or similar chemicals with serious side effects
Pineal Gland: secretes melatonin (primarily at night)
- melatonin appears to be involved in maintenance or circadian rhythms or sleep/wake (day/night) cycles
- pineal gland may also be involved in human sexual development; children in whom a brain tumor has destroyed the pineal gland experience puberty earlier
Thymus: lobular gland just beneath the sternum (above heart) in upper thoracic cavity
- secretes thymopoietins & thymosins; involved with normal development and differentiation of T cells (lymphocytes)
- it reaches its largest size and is most active during childhood; with age, it shrinks and becomes fatty
Prostaglandins: potent chemical signals produced in cells from arachidonate, a fatty acid
- they are not distributed in the blood but act locally
- in the uterus, prostaglandins cause the uterus to contract and are implicated in menstrual discomfort
- aspirin reduces temperature and controls pain because of its effect on prostaglandins
Chapter 43: Reproduction
How Animals Reproduce
- there are two patterns of reproduction:
o asexual–only one parent is involved
o sexual–two parents are involved
- Asexual Reproduction: most use a combination of sexual and asexual
o hydra undergo budding; a new individual arises as an outgrowth (bud) of a parent
o Obelia polyps produce a medusa by budding; the medusa the produces eggs and sperm
o flatworms can constrict and pinch off
o fragmentation followed by regeneration is seen among sponges and echinoderms
o parthenogenesis is found among some insects, worms, fish, lizards and some other animals; the egg develops without fertilization
o in honeybees, the queen can decide to fertilize or not fertilize the eggs, producing diploid female workers or haploid male drones
- Sexual Reproduction: the egg of one parent is fertilized by the sperm of the other
o hermaphroditic organisms possess both male and female organs
§ a pair of earthworms cross-fertilize each other
§ sex reversal involves the changing of sex; a male wrass (a reef fish) has a harem but if the male dies, the largest female becomes a male
o gonads are organs specialized to produce gametes
o there are two types of gonads: testes produce sperm and ovaries produce eggs
o eggs and sperm cells derive from germ cells specialized for this development
o other cells in the gonads support and nourish the developing gametes or produce hormones for reproduction
o accessory organs form ducts and storage areas that aid in uniting gametes
o sexually-reproducing animals have various methods to ensure that the gametes find each other
§ aquatic animals that practice external fertilization synchronize egg release
§ the lunar cycle is one trigger that cues animals by tides
§ hundreds of thousands of palolo worms rise to the surface to release eggs during a 2-4 hour period
o copulation is sexual union to facilitate the reception of sperm by a female
§ the penis is a male copulatory organ typical of terrestrial males; it deposits sperm into the female¹s vagina
§ aquatic animals have other types of copulatory organs or employ other strategies for delivering sperm: 1) Lobsters and crayfish have modified swimmerets. 2) Cuttlefish and octopuses use an arm. 3) Sharks have a modified pelvic fin to pass packets of sperm to the female shac. Birds lack a penis and vagina; they transfer sperm from cloaca to cloaca
- Life History Strategies
o many aquatic animals use external fertilization; eggs and sperm join outside the body in the water
o terrestrial animals tend to practice internal fertilization; eggs and sperm join inside the female¹s body
o both are usually oviparous; they deposit eggs in the external environment
o insect eggs are produced in ovaries; they mature and increase in size as a result of the accumulation of yolk
§ yolk is stored food to be used by the developing embryo
§ to prevent insect eggs from drying out, their eggshell has several layers of protein or wax
§ in insects, small holes are left at one end to allow for the entry of sperm
o some insects have a special organ to store sperm so the eggs can be fertilized later
o larval stage is often different in appearance and way of life from the adult form
§ the larva is able to seek its own food to sustain itself until it becomes an adult
§ metamorphosis: a major change in form in some animals during development
§ incomplete metamorphosis lacks pupal stage and nymphs look like adults
§ larval aquatic forms can utilize a different food source than the adults
§ bilaterally symmetrical sea star larvae attach to a substrate and become radially symmetrical adult
§ free-swimming barnacle larvae metamorphose into sessile adults with calcareous plates
§ crayfish lacks a larval stage; eggs hatch into tiny juveniles resembling adults
o reptiles and birds provide their eggs with plentiful yolk; there is no larval stage
§ complete development takes place within a shell containing extraembryonic membranes
§ the chorion is the outermost membrane that lies next to the shell and functions in gas exchange
§ the amnion forms a water-filled sac around embryo that prevents drying out
§ a yolk sac holds yolk which nourishes the embryo
§ the allantois holds nitrogen waste products
§ a shelled egg frees an animal from any need to reproduce in water and also helps it live completely on land
o birds tend their eggs: newly hatched birds have to be fed before they develop to where they can seek food on their own
§ parent bird¹s behaviors involve complex hormonal and neural regulation
o in oysters and sea horses, eggs remain inside the body and hatch fully-developed
o garter snakes, water snakes, and pit vipers also retain eggs until they hatch and give birth to live young
o mammals are viviparous; embryo remains in female¹s body during development
§ the nutrients needed for development are constantly supplied by the mother
§ viviparity represents the ultimate in caring for the zygote and the embryo
§ the evolution of viviparity can be seen in the primitive mammals. 1) The exceptions are the duckbill platypus and the spiny anteater, which are egg-laying mammals. 2) Marsupials give birth to immature offspring that finish developing within a pouch. 3) In all other mammals, development occurs in a placenta
o the placenta is a complex organ comprised of maternal and embryonic tissues. a. A placenta exchanges O2, CO2, nutrients, wastes, etc., between the fetal and maternal circulations. b. Evolution allowed embryos to exchange materials with the mother; this made the shell unnecessary
Male Reproductive System
- Male Gonads: paired testes are suspended in the scrotal sacs of the scrotum
o the testes began development in the abdominal cavity but descend into the scrotal sac during development
o if the testes do not descend, without surgery or hormonal therapy, sterility results
o the lower temperature of the scrotum is vital to normal sperm production
- sperm produced in the testis mature within the epididymis - a tightly coiled tubule outside of the testis in which the sperm undergo maturation (gain ability to swim)
o mature sperm are propelled into the vas deferens by muscular contractions
o sperm are stored in both the epididymides and the vasa deferentia
o when a male is sexually aroused, the sperm enter the urethra, part of which extends through the penis
o the penis is a copulatory organ used to introduce sperm into the female vagina
§ three columns of spongy, erectile tissue extend down the penile shaft
§ during sexual arousal, nervous reflexes cause an increase in the arterial blood flow to the penis (nitric oxide released is vasodilator)
§ increased blood flow fills and distends the erectile tissue, and the penis stiffens and increases in size
§ these changes cause an erection; impotency is failure to achieve an erection
o semen (seminal fluid) is thick, white fluid containing sperm and glandular secretions
§ semen is formed by seminal vesicles, prostate gland, and bulbourethral gland
§ the seminal vesicles lie at the base of the urinary bladder. 1) Each joins a vas deferens to form an ejaculatory duct that enters the urethra. 2) They secrete into the ejaculatory duct a thick fluid containing nutrients for use by the sperm
§ the prostate gland is located just below the urinary bladder and surrounds the upper portion of the urethra. 1) It secretes a milky, slightly alkaline solution that promotes sperm motility and viability. 2) In older men, the prostate gland may become enlarged and constrict the urethra. 3) Prostate cancer is also common in older men
§ the bulbourethral glands are located below the prostate gland and on either side of urethra; they release mucus secretions that provide lubrication
o the urethra also conducts urine from the bladder during urination
- ejaculation results in expulsion of semen at the peak of sexual arousal
o the first phases of ejaculation is emission sending sperm with seminal fluid into the ejaculatory duct
o the second phase of ejaculation is expulsion where rhythmic muscular contractions release semen from the urethra
o a refractory period follows when stimulation does not bring about erection
o orgasm is the physiological and psychological sensations that occur at the climax of sexual stimulation.
- the testes are divided into lobules, each of which contains 1-3 seminiferous tubules
o spermatogenesis, a process of meiosis, produces sperm cells
o the sustentacular (Sertoli) cells support, nourish, & regulate spermatogenic cells
o mature sperm (spermatozoa) have three parts: the sperm head contains a nucleus covered by an acrosome which stores enzymes to penetrate egg; the middle piece contains mitochondria that provide the energy for movement; the tail contains microtubules as components of a flagellum; its movement propels sperm
o the ejaculate of a normal human male contains several hundred million sperm
o fewer than 100 reach the egg; and only one sperm normally enters an egg
- Hormonal Regulation in Males
o the hypothalamus has ultimate control of the testes¹ sexual function through secreting of gonadotropic-releasing hormone (GnRH) that stimulates the pituitary to produce gonadotropic hormones
o follicle-stimulating hormone (FSH) stimulates spermatogenesis
o luteinizing hormone (LH) stimulates testosterone secretion by interstitial cells
o the seminiferous tubules also release the hormone inhibin
o the hypothalamus-pituitary-testis system are involved in a negative feedback relationship that maintains a fairly constant production of sperm and testosterone
- Functions of Testosterone: testosterone is main sex hormone in males
o testosterone is essential for the development of male secondary sex characteristics and for the maturation of sperm
o testosterone is also involved in triggering baldness if baldness genes are present
Female Reproductive System
- Internal Reproductive System: the female reproductive system includes: ovaries, oviducts, uterus, and vagina
o the ovaries produce a secondary oocyte each month; the ovaries are located in the abdominal cavity
§ the ovaries produce both the egg (ovum) and the female sex hormones, estrogens and progesterone, during the ovarian cycle
o the oviducts (Fallopian tubes) extend from the ovaries to the uterus
§ the oviducts are not attached to the ovaries
§ fingerlike projections called fimbriae sweep over the ovaries and waft in the egg when it erupts
§ this is the normal site for fertilization; the embryo is slowly moved by ciliary movement toward the uterus
o the uterus is a hollow, thick-walled muscular organ the size and shape of an inverted pear. a. Embryo completes development by embedding itself in uterine lining, the endometrium. b. The narrow end of the uterus is the cervix. c. A small opening at the cervix of the uterus leads to the vaginal canal
o the vagina is a tube at a 45 angle with the small of the back
§ its mucosal lining lies in folds and it can extend, as necessary in childbirth
§ it receives the penis during copulation and also serves as the birth canal
- the external genitalia of women are known collectively as the vulva
o the mons pubis, labia minora, and labia majora are to the side of the vaginal and urethral openings
o at the front juncture of the labia minora is the clitoris; this is homologous to the penis in males
o the clitoris has a short shaft of erectile tissue and is capped by a pea-shaped glans
o it contains many sensory receptors that allow it to function as a sexually sensitive organ
o orgasm involves the release of neuromuscular tension in the muscles of the genital area, vagina, and uterus
- The Ovarian Cycle
o a female is born with as many as two million follicles; the number is reduced to 300,000–400,000 by the time of puberty; and only a small number of follicles (about 400) ever mature
o as a follicle matures, it develops from a primary follicle to secondary follicle to a vesicular (Graafian) follicle
o as oogenesis is occurring; a secondary follicle contains a secondary oocyte pushed to one side of fluid-filled cavity
o the vesicular follicle fills with fluid until the follicle wall balloons out on the surface and bursts, releasing a secondary oocyte surrounded by a zona pellucida and follicular cells
o ovulation is the rupture of the vesicular follicle with the discharge of the secondary oocyte into pelvic cavity
o the secondary oocyte completes a second meiotic cell division upon fertilization
o meanwhile, the follicle develops into the corpus luteum; if pregnancy does not occur, the corpus luteum begins to degenerate in 10 days
o the ovarian cycle is under the control of gonadotropic hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
o during the follicular phase, FSH promotes the development of a follicle that secretes estrogen
o as the estrogen level in the blood rises, it exerts feedback control over the anterior pituitary secretion of FSH; the follicular phase comes to an end
o estrogen levels in the blood rise, causing the hypothalamus to secret more GnRH; this causes a surge in LH secretion
o the LH spike then triggers ovulation
o the luteal phase is the second half of the ovarian cycle following ovulation
§ LH promotes the development of the corpus luteum, which secretes large amounts of progesterone
§ progesterone causes the endometrium to maintain
§ as the blood level of progesterone rises, negative feedback to anterior pituitary¹s secretion of LH causes the corpus luteum to degenerate
§ as the luteal phase ends, menstruation occurs
- The Uterine Cycle: estrogens and progesterone affect the endometrium of the uterus to cause a cycle of events known as the uterine cycle
o an average 28-day uterine cycle is divided into four sections
§ during days 1–5, low levels of estrogen and progesterone in the body cause menstruation - the periodic shedding of tissue and blood (collectively called menses) from the endometrium out of the vagina
§ during days 6–13, an increased production of estrogens by an ovarian follicle causes the endometrium to thicken and become vascular and glandular (proliferative phase)
§ ovulation usually occurs on day 14 of the 28-day cycle
§ gays 15–28 see increased production of progesterone by the corpus luteum that causes the endometrium to double in thickness; uterine glands mature, producing a thick mucoid secretion (secretory phase)
· the endometrium is now prepared to receive a developing embryo
· if no pregnancy occurs, the progesterone and estrogen levels decline and the corpus luteum and uterine lining degenerate
o the ovarian cycle controls the uterine cycle
- Events Following Fertilization: if fertilization occurs, the embryo begins development as it travels down the oviduct to the uterus
o embryo becomes embedded in the endometrium several days after fertilization
o the placenta develops from both maternal and embryonic tissues
§ the placenta functions to exchange gases and nutrients between the fetal and maternal circulation
§ there is normally no mixing of blood between maternal and fetal circulations
o initially, the placenta produces human chorionic gonadotropin (hCG) which maintains the corpus luteum
o progesterone and estrogens have two effects at this stage:
§ they shut down the anterior pituitary so that no new follicles mature
§ they maintain the lining of the uterus so the corpus luteum is not needed
o there is no menstruation during pregnancy
- Functions of Estrogen and Progesterone
o estrogens maintain the normal development of the related organs and are responsible for the secondary sex characteristics of females
o there is less body and facial hair, and more fat beneath the skin provides a more rounded appearance
o the pelvic girdle enlarges and the pelvic cavity is larger (women have wider hips
o both estrogen and progesterone are required for breast development
- The Female Breast contains 15–24 lobules, each with a mammary duct
o the mammary duct begins at the nipple and divides into numerous ducts which end in alveoli (blind sacs)
o prolactin hormone is needed for lactation (milk production) to begin
o production of prolactin is suppressed by the feedback inhibition that estrogens and progesterone have on the anterior pituitary during pregnancy
o therefore it takes a couple of days after delivery for milk production to begin
o the breasts produce a watery, yellowish white fluid (colostrum) similar to milk but containing more protein and less fat, and it is rich in IgA antibodies providing some immunity to a newborn
o breast cancer is the most common form of cancer in females; women should have regular breast checks and mammograms when recommended