Biology 102

Study Notes Exam 5

 

Chapter 38: Body Fluid Regulation and Excretion

 

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


Chapter 42: Hormones and the Endocrine System

 

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

§