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
§