Unit 4 - Homeostasis Flashcards
homeostasis
- consists of mechanisms to ensure an ideal/constant internal cellular and biocemical environment
- ensures proper cellular/systemic function
components of homeostatic mechanisms
- detector
- decision-maker
- action(s) center
homeostatic feedback mechanisms
negative
- most common in homeostatic feedback loops
- alter the result (opposite effect)
positive
- augments the result (same effect)
- e.g. during labour, uterine muscle contractions increase in force and frequency, via oxytocin
- e.g. during lactation, milk is released in increasing frequencies
examples of homeostatic processes
thermoregulation
- ensures a constant internal temperature of 37°C is maintained
- hypothalamus acts as an “internal thermostat”; detects thermal changes
- e.g. goosebumps, shiver (thermogenesis), and vasoconstriction when it’s too cold
- e.g. sweating and vasodilation when it’s too hot
blood glucose regulation
- pancreas produces insulin to lower glucose levels in our blood (and to increase glycogen levels in the liver), when glucose levels are too low
- pancreas produces glucagon to increase glucose levels in our blood, by breaking down glycogen (in the liver) into glucose molecules, when glucose levels are too high
urine production
- is a dynamic process; partiality exists
- composed of 3 main parts:
1. filtration
2. re-absorption
3. secretion
flow of urine in the Bowman’s capture
filtration
flow of urine in the proximal tubule
- passive reabsorption of HCO3-, H2O, and K+
- active reabsorption of NaCl and nutrients (amino acids and glucose)
- active secretion of H+
- passive secretion of NH3
flow of urine in the decending limp of the loop of Henle
passive reabsorption of H2O
flow of urine in the ascending limp of the loop of Henle
passive and active reabsorption of NaCl
flow of urine in the distal tubule
- active reabsorption of NaCl and HCO3-
- passive reabsorption of H2O
- active secretion of K+ and H+
flow of urine in the collecting duct
- active secretion of urea, uric acid, and ammonia
- active reabsorption of NaCl
- passive reabsorption of H2O
kidney functions
- eliminates osmotic pressure (water balance)
- eliminates toxic metabolites (e.g. urea, uric acid)
- produces certain hormones (is an endocrine organ)
the nephron
the functional unit of the kidney
major parts of the nephron:
1. Bowman’s capsule
2. proximal tubule
3. descending loop of Henle
4. ascending loop of Henle
5. distal tubule
6. collecting duct
filtrate
- premature urine found in the Bowman’s capsule
- doesn’t contain red or white blood cells
- contains H2O, glucose, amino acids, and Na+, Cl-
osmotic pressure
is when particles bump against the walls of arteries, veins, etc.; is proportional to the amount of solutes in the blood (solvent)
osmotic pressure regulation
When blood osmotic pressure is too high (e.g. sweathing, dehydration)…
1. Osmoreceptors located in the hypothalamus detect changes in osmotic pressure.
2. Cells of the hypothalmus shrink; the nerve message is sent to the pituitary gland.
3. The pituitary gland stores and releases antidiuretic hormone (ADH) into the blood, and then to the kidneys; increasing the permeability of the distal tube and collecting duct, and therefore increasing H2O absorption.
4. There is a behavioural response: the sensation of thirst.
5. Drinking water lowers the osmotic pressure of blood.
6. Increased H2O reabsorption prevents the osmotic pressure of bodily fluids from increasing any further and prevents dehydration.
7. The collecting duct carries urine from the nephrons, to the pelvis of the kidney.
blood pressure regulation
When blood pressure/volume is too low (e.g. dehydration, blood loss)…
1. Specialized cells in the juxtaglomerular apparatus of the kidney release renin.
2. Renin converts angiotensinogen (a plasma protein) into angiotensin.
3. Angiotensin causes vasoconstriction of blood vessels.
4. Angiotensin stimulates the release of aldosterone from the adrenal gland. Aldosterone is carried in blood to the kidneys, and acts on the nephrons to increase Na+ and H2O reabsorption.
acid-base buffer system
When blood pH is too acidic (excess hydrogen ions), bicarbonate ions are used to buffer the blood (H+ + HCO3- → H2CO3).
When blood pH is too basic (excess hydroxide ions), carbonic acid is used to buffer the blood (OH- + H2CO3 → HCO3- + H2O).
blood pH regulation in respiration
When blood pH is too basic, a decreased breathing rate leads to a higher number of hydrogen ions (H2O + CO2→ H2CO3 →H+ + HCO3-).
When blood pH is too acidic, an increased breathing rate leads to more carbon dioxide exhaled, and a reduced number of hydrogen ions (H+ + HCO3- → H2CO3 → H2O + CO2).
blood pH regulation in kidneys
When blood pH is too basic…
1. HCO3- is reabsorbed.
2. H+ is excreted as needed to maintain the pH of the blood.
3. Excess hydrogen ions are buffered, for example, by ammonia which is produced in tubule cells by the breakdown of amino acids (NH3 + H+ → NH4+).
kidney diseases
- diabetes mellitus
- diabetes insipidus
- Bright’s disease
- kidney stones
- chronic renal impairment diseases
diabetes mellitus
- caused by inadequate secretion of insulin from β cells of islets of Langerhans in the pancreas
- without insulin, blood sugar levels rise; excess sugar remains in the nephron (sweet urine)
- greater osmotic pressure; H2O reabsorption is reduce
- large volumes of urine voided (dehydration and fatigue)
- includes type I (congenital), type II (developed during adulthood; 40+ years), and gestational diabetes
- metformin is commonly used to treat type II and gestational diabetes
- Banting and Best succesfully isolated insulin and treated a diabetic child
diabetes insipidus
- caused by the destruction of the ADH-producing cells in the hypothalamus, or the destruction of nerve tracts between the hypothalamus and the pituitary gland
- without ADH to regulate H2O reabsorption, urine output increases dramatically
Bright’s disease
- a.k.a. nephritis
- isn’t a single disease, but is a broad description of many diseases characterized by inflammation of the nephrons
- one type of nephritis is “glomeralitis” (inflammation of the glomerulus)
- proteins and other larger molecules pass into the nephron
- urine output increased (dehydration; lack of activity)
kidney stones
- caused by the precipitation of mineral solutes (Ca2+) from the blood
- categorized as either alkaline stones or acid stones
- delicate tissues are torn as the move toward the bladder; causes excruciating pain
dialysis technology
- restores the proper solute balance for people with inefficient kidneys
- dialysis is the exchange of substances across a semipermeable membrane
- operates on the principles of diffusion and blood pressure
- includes hemodialysis and continuous ambulatory peritoneal dialysis
hemodialysis
- connected to the patient’s circulatory system by a vein
- blood pumped through various dialysis tubes
- urea and other wastes are continuously removes, via the continuous flushing of expended dialysis solution
- the body also receives hormones the kidneys are unable to produce
continuous ambulatory peritoneal dialysis (CAPD)
- 2 L of dialysis fluids are pumped into the abdominal cavity
- wastes diffuse from the plasma into the peritoneum and the dialysis fluid
- wastes accumulate in the dialysis fluids, and can be drained off and replaced several times a day
- CAPD allows for greater independence because the process can be done on your own at home
endocrinology
the study of hormonal action (e.g. insulin)
hormones
chemical messengers that signal other cells, via the circulatory system
exocrinology
the study of external secretions (e.g. sweat glands, gastric cells; pepsin)
paracrine signalling
involves factors (molecules) that signal adjacent cells
autocrine signalling
involves factors (molecules) that signal the same cell (e.g. stem cells partake in differentiation)
how steroid hormones work
- The hormone diffuses from the cell.
- The hormone diffuses into the target cell (steroids are hydrophobic lipids, and therefore pass through the fat-soluble lipid bilayer) and attaches to the cytosolic receptor.
- The hormone-receptor complex moves into the nucleus and attaches to DNA.
- A gene is activated in the DNA, and protein synthesis is initiated.
how protein hormones work
- The hormone is released from the cell.
- The hormone attaches to a surface receptor on the outside of the cell membrane.
- The hormone-receptor complex promotes the formation of cyclic AMP (cAMP), through ATP.
- cAMP acts as a messenger to activate enzymes; biochemical pathways are triggered (signal transduction).
chemical signalling
- The endocrine system maintains signals over long distances and for long periods of time (from endocrine cells to target cells, via the bloodstream).
- The nervous system uses rapid signalling; the neuron releases neurotransmitters (small proteins of 10-20 amino acids) via electrochemical impulses (action potential). The neurotransmitter diffuses across a gap called the synapse to target cells.
endocrine glands
- hypothalamus
- pituitary gland/hypophysis (includes anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis))
- thyroid
- parathyroid
- adrenal gland (includes adrenal medulla and adrenal cortex)
- pancreas
- kidneys
- female ovaries
- male testes
gonadotropin-releasing hormone (GnRH)
secreted by the hypothalamus to the anterior pituitary to release FSH and LH to the testes and ovaries
hormones secreted by the anterior pituitary
- growth hormone
- prolactin
- FSH
- LH
- TSH
- ACTH
human growth hormone (hGH)
secreted by the anterior pituitary to most other cells for growth and cell division
prolactin (PRL)
secreted by the anterior pituitary to mammary glands to stimulate milk production
follicle-stimulating hormone (FSH)
secreted by the anterior pituitary to the testes or ovaries
- in males, it is sent to the testes; stimulating sperm production and releasing inhibin
- in females, it is sent to the ovaries; stimulating the production of estrogen
inhibin
secreted by the seminiferous tubules of the testes to the anterior pituitary and the hypothalamus to produce a negative feedback loop that inhibits FSH production (and subsequently sperm production)
luteinizing hormone (LH)
secreted by the anterior pituitary to the testes or ovaries
- in males, it is sent to the testes; stimulating testosterone production
- in females, it is sent to the ovaries; triggering ovulation and stimulating progesterone production
thyroid-stimulating hormone (TSH)
secreted by the anterior pituitary to stimulate the thyroid gland
adrenocorticotropic hormone (ACTH)
secreted by the anterior pituitary to stimulate the adrenal cortex
hormones secreted by the posterior pituitary
- ADH
- oxytocin
antidiuretic hormone (ADH)
secreted by the posterior pituitary to the kidneys to promote H2O reabsorption
oxytocin
secreted by the posterior pituitary to the mammary glands to release human milk, and to the uterus to stimulate uterine muscle contractions
hormones secreted by the thyroid
- tyroxine
- calcitonin
tyroxine (T4)
secreted by the thyroid and released into the bloodstream to control the rate of metabolism
hypothyroidism
condition resulting when the thyroid produces extremely low levels of thyroxine
hyperthyroidism
condition resulting when the thyroid produces extremely high levels of thyroxine
goitre
enlargement of the thyroid gland that occurs when the thyroid is constantly stimulated by TSH, but is unable to synthesize thyroxine
thyroid gland regulation
- The hypothalamus secretes a releasing hormone that stimulates the anterior pituitary gland.
- The anterior pituitary releases TSH into the bloodstream.
- TSH targets the thyroid gland.
- TSH causes the thyroid to secrete thyroxine into the bloodstream. Thyroxine stimulates increased cellular respiration in target cells throughout the body.
- High levels of thyroxine cause negative feedback on the pituitary and hypothalamus, shutting
down production of TSH.
blood calcium regulation
When blood Ca2+ too high…
1. The thyroid gland secretes calcitonin into the blood.
2. Bones take up Ca2+ from the blood.
3. Blood Ca2+ lowers.
When blood Ca2+ too low…
1. The parathyroid gland releases parathyroid hormone (PTH) into the blood.
2. Intestines absorb Ca2+ from the digestive tract.
3. Kidneys reabsorb Ca2+ from kidney tubules.
4. Bones release Ca2+ into the blood.
5. Blood Ca2+ rises.
epinephrine and norepinephrine (adrenaline)
secreted by the adrenal medulla; stimulate flight-or-flight responses:
- increase in blood glucose due to glycogen that has been converted into glucose
- increase in heart rate, breathing rate, and cell metabolism
- change in blood flow patterns that direct more blood to heart and muscle cells (vasodilation in leg/arm muscles; vasoconstriction in GI tract)
mineralocorticoids
secreted by the adrenal cortex to promote reabsorption of sodium and water by the kidneys
glucocorticoids
secreted by the adrenal cortex to raise blood glucose levels via the breakdown of proteins and fats into glucose; there is a subsequent suppression of the inflammatory response of the immune system
hormones secreted by the pancreas
- insulin
- glucagon
insulin
secreted by the pancreas to lower blood glucose levels and promote the formation of glycogen in the liver
glucagon
secreted by the pancreas to raise blood glucose levels by converting glycogen in the liver to glucose
renin
secreted by the kidneys to stimulate the secretion of aldosterone from the adrenal cortex
estrogen
secreted by the follicles of the ovaries to the rest of the body to stimulate the development of the female reproductive tract and secondary sex characteristics
progesterone
secreted by the corpus luteum of the ovary to prepare the uterus for the fertilized egg (ovum), and later, by the placenta to maintain pregnancy
testosterone
secreted by the interstitial cells of the testes to the rest of the body to stimulate the development of the male reproductive tract and secondary sex characteristics
andropause
a gradual decline in males’ testosterone levels, beginning around 40 years old
menopause
a period in females’ life, around 50 years old, when a decrease in estrogen and progesterone levels leads to an end of menstrual cycles
blood glucose regulation
When blood sugar is too high (after a meal)…
1. β-cells of the islets of Langerhans in the pancreas release insulin into the blood.
2. The liver converts glucose to glycogen, and stores it.
3. Body cells become permeable to glucose.
4. Blood glucose levels decrease to a normal level.
When blood sugar is too low (after fasting)…
1. α-cells of the islets of Langerhans in the pancreas release glucagon into the blood.
2. The liver converts glycogen to glucose, and releases it into the blood..
3. Blood glucose levels increase to a normal level.
ovarian cycle
- Developing follicles produce estrogen, and a little progesterone.
- The mature follicle releases the ovum at ovulation.
- The corpus luteum produces progesterone, and a little estrogen.
- The corpus luteum degenerates.
menstrual cycle
- Flow phase (days 1-5): The menstrual (and ovarian cycle) starts with menstruation. The corpus luteum has degenerated, and sex hormone levels are low. The endometrium is also very thin at this time.
- Follicular phase (days 6-14): As a new follicle starts to mature, estrogen levels rise enough for the endometrium to start to thicken.
- Luteal phase (days 15-28): After ovulation, the release of progesterone in the corpus luteum causes the endometrium to thicken rapidly, almost doubling or tripling in thickness. If fertilization does not occur, the corpus luteum degenerates, sex hormone levels start to drop, and menstruation marks the beginning of the cycle once again.
divisions of the nervous system
The peripheral nervous system consists of the somatic nervous system, involved in conscious (voluntary) actions, and the autonomic nervous system, involved in non-conscious (involuntary) actions.
somatic nervous system:
- Sensory fibers carry information from the body to the brain (e.g. pressure, pain, temperature, vision).
- Motor fibers carry information from the brain to the body (e.g. nerve fibers connected to muscles).
autonomic nervous system
- Sympathetic fibers prepare the body in a state of alertness (e.g. pupil dilation).
- Parasympathetic fibers prepare the body in a state of relaxation (e.g. increased rate of digestion, pupil constriction).
The central nervous system consists of the brain and spinal cord.
motor vs. sensory neurons
motor neuron
- inside the central nervous system
- transmits impulses from the central nervous system to an effector to help you move and function
sensory neuron
- inside the peripheral nervous system
- information is transmitted to the brain to help you touch, taste, smell, and see
the reflex arc
- A stimulus causes action potentials in the sensory receptor.
- The message travels along sensory axon.
- The message travels along sensory dendrite.
- The message reaches interneuron dendrite.
- The message splits: one to brain, one to motor neuron dendrite.
- The message travels along motor axon.
- The message causes muscle to contract.
electrochemical impulse
signal propagation within a membrane (action potential)
action potential
the voltage difference across an excited nerve cell membrane (potential difference = voltage)
steps of action potential
- resting potential (polarization): The membrane is polarized (-70mV). The axonal membrane is 50x more permeable to K+ than to Na+ (K+ efflux > Na+ influx). The axoplasm is relatively negative compared to the E.C.F.
- depolarization: The Na+ channels open and there is a N+ influx. The axoplasm becomes more positive than the E.C.F.. The membrane is depolarized (+40mV).
- repolarization: The K+ channels open and there is a K+ efflux. The axoplasm becomes more negative than the E.C.F.. The membrane is repolarized (-70mV).
- refractory period: The sodium-potassium pump actively pumps 3 Na+ out and 2 K+ in.
- hyperpolarization: When K+ channels open before Na+ channels. This is an inhibitory impulse (-90mV).
threshold level
the minimum level of a stimulus necessary to produce a response
summation
effect produced by the accumulation of two or more neurotransmitters from two or more neurons
all-or-none response
a nerve or muscle fibre responds completely or not at all to a stimulus (the magnitude of summation doesn’t correlate to the frequency of action potentials)
synaptic transmission
- The impulse reaches synapse from the axon.
- The impulse stimulates synaptic vesicles to move to the presynaptic membrane.
- The synaptic vesicles dump neurotransmitter substance into the synaptic cleft.
- The neurotransmitter substance diffuses across the cleft.
- The neurotransmitter substrance fits into the receptor sites on the postsynaptic membrane.
- An enzyme cleaves the neurotransmitter substance and clears out the synaptic cleft (e.g. acetylcholinesterase breaks down acetylcholine into acetic acid and choline).
- An action potential is stimulated at the postsynaptic membrane and the impulse travels down the dendrite.
nerve agents
- substances that block the enzyme that clears out the synaptic cleft; allow for continuous stimulation
- result in muscle spasms and potentially death
- e.g. sarin gas
meninges
protective membranes that surround the brain and spinal cord
from outermost to innermost:
dura mater
↓
arachnoid mater
↓
pia mater
cerebrospinal fluid (C.S.F.)
acts both as a shock absorber and a transport medium; provides a connection between neural and endocrine systems
olfactory bulb
processes sensory information relating to smell
cerebrum
largest and most highly developed part of the brain
cerebral cortex
outer lining of the cerebral hemispheres
corpus callosum
a bundle of nerves that joins the two cerebral hemispheres: the left side (verbal skills), and the right side (spatial awareness)
the lobes of the cerebrum
frontal lobe
- largest lobe in the human brain
- associated with motor control
temporal lobe
- associated with processing auditory information
parietal lobe
- associated with processing sensory information
occipital lobe
- associated with vision and interpreting visual information
thalamus
processes and interprets sensory information and directs it to the cerebrum
cerebellum
involved in fine motor control, balance, and smooth muscle contractions (“muscle tone”)
pons
means “bridge” (pont); acts as a relay station by sending nerve messages to other parts of the brain
medulla oblongata
joins the spinal cord to the cerebellum; controls autonomic muscle action (e.g. breathing, heart beating)
positron-emission tomography (PET)
- water, glucose, or another molecule is labelled with a radioactive isotope and injected into the patient’s bloodstream
- the radioactive compound goes to the most active parts of the brain and the radiation is detected by a PET camera connected to a computer
- PET scans are used to evaluate brain disorders, heart problems, and certain cancers
magnetic resonance imaging (MRI)
- takes advantage of the behaviour of hydrogen atoms in water molecules
- uses powerful magnets to align the nuclei, and briefly knock them out of alignment with a pulse of radiowaves
- the hydrogen nuclei spring back into alignment, emitting faint radio signals that are detected by the MRI scanner and the translated into a computer image
- MRI scans are used to detect problems in the brain and spinal cord (e.g. strokes)
- functional MRI (fMRI) scans measure brain function rather than brain structure
computerized tomography (CT)
- produces 3D images of thin X-ray sections through the body
- CT scans are used to detect ruptured blood vessels and bone trauma
