d3.3 (homeostasis) Flashcards
regulation of homeostasis relies on what mechanism?
negative feedback loops (the response to some stimulus affecting the variable is corrective)
5 examples of - feedback loops in homeostasis in humans
heart rate
blood pH
blood glucose
body temperature
blood osmolality
3 examples of + feedback loops in homeostasis in humans
blood clotting triggers more blood clotting
uterus contractions trigger more uterus contractions during childbirth
a cancer cell will cause there to be more cancer cells
define endotherm
organisms that generate heat internally to maintain a steady body temperature (examples: birds and mammals)
define ectotherm
organisms that rely on external heat sources to regulate their body temperature (examples: lizards and most fish)
define thermoregulation
the maintenance of a core body temperature despite fluctuations in external temperatures by balancing heat generation with heat loss
thermoregulators maintain body temperature homeostasis via negative feedback mechanisms. what are 2 responses to heat?
vasodilation (widening of blood vessels)
sweating
thermoregulators maintain body temperature homeostasis via negative feedback mechanisms. what are 4 responses to cold?
vasoconstriction (contracting of blood vessels)
shivering
uncoupled respiration (a process that dissipates energy instead of using it to perform work)
piloerection (goosebumps)
5 steps of negative feedback in overly hot conditions
1 (stimulus): body temperature rises due to exercise or hot environment
2 (receptor): thermoreceptors in the skin and central nervous system sense rise in body temperature
3 (control center): hypothalamus activates responses
4 (effector): blood vessels dilation and sweat glands are activated
5 (response): heat is lost from the body, decreasing body temperature
5 steps of negative feedback in overly cold conditions
1 (stimulus): cold environment causes heat to leave the body
2 (receptor): thermoreceptors in the skin and central nervous system sense drop in body temperature
3 (control center): hypothalamus activates responses
4 (effector): blood vessels constrict, shivering is activated and metabolism increased
5 (response): more heat generated and less is lost from the body, increasing body temperature
what are the effectors & their roles in body temperature homeostasis? x6
pituitary: releases a hormone that stimulates the thyroid gland to release thyroxin
thyroid: increase or decrease release of the hormone thyroxin to change basal metabolic rate
adipose tissue: brown fat cells generate heat through uncoupled cellular respiration
blood vessels: constrict or dilate to carry more or less blood towards different regions of the body
muscles: respond to signals to contract, causing shivering, hair erection and changes to ventilation rate
sweat glands: activate sweating to reduce body temperature via evaporative cooling
what are thermoreceptors?
ion channel proteins in the membrane of specific sensory neurons that help the body detect changes in temperature
how do thermoreceptors work upon a change in temperature? x5 steps
- channels open
- flow of ions
- cell membrane depolarization
- electrical impulses propagated along nerve fibres
- conveyed to the brain (hypothalamus)
what is the thyroid?
an endocrine gland located in the front of the neck, made up of two lobes that sit on either side of the trachea (wind pipe), connected by a narrow strip of tissue
how are cells triggered to increase their metabolic rate in body temperature homeostasis? x4 steps
- thermoreceptors sense a change in temperature and send a signal to the hypothalamus
- hypothalamus causes pituitary to increase secretion of TSH (thyroid stimulating horomone)
- TSH causes the thyroid will secrete a hormone called thyroxine
- thyroxine travels to target cells throughout the body, triggering the cells to increase their metabolic rate by binding to the cell’s intranuclear receptor
how does brown adipose tissue produce heat?
uncoupled cellular respiration
define uncoupled cellular respiration
a metabolic process where the mitochondria actively dissipate energy as heat instead of producing ATP
how does uncoupled cellular respiration work?
uncoupling protein 1 (UCP1) allows protons to leak across the inner mitochondrial membrane, instead of flowing back in through ATP-synthase
energy carried by protons is released as heat as it passes through UCP1
(watch a video on this)
how does shivering work?
skeletal muscles rapidly contracting and relaxing. the heat generation from muscle contractions plays a crucial role in maintaining body temperature
why do muscles produce heat when contracting?
the process of muscle contraction relies on the breakdown of ATP molecules, which is an exothermic reaction, meaning it releases heat energy
how does sweat cool us?
when sweat evaporates from the skin, it cools the body through a mechanism called evaporative cooling (as water evaporates, it absorbs heat energy from the skin, removing heat from the body).
(watch a video on this)
how does piloerection occur?
the contraction of muscles at the base of hair follicles that causes hair to stand up
the erect hairs act as a thermal insulator; the thick coat traps the warm air radiating from the body
how does blood movement cool us?
distributes heat energy generated through metabolism throughout the body
how does vasodilation occur?
muscles within the artery wall relax, causing the diameter of the artery to widen and an increase in blood flowing through the vessel
how does vasoconstriction occur?
muscles within the artery wall contract, causing the diameter of the artery to narrow and a decrease in blood flowing through the vessel (decreases heat loss)
why do vasodilation and constriction need to be balanced?
for overall blood pressure to be constant
___ and ___ can withstand the largest blood volume changes
skeletal muscle and digestive system
___ and ___ can only tolerate very small decreases in their blood supply
brain and kidneys
what arteries supply blood to the brain? x2
internal carotid arteries and vertebral arteries
vertebral arteries join to form the ___
basilar artery
_____ and _____ branch out to form the circle of willis
basilar artery and internal carotid arteries
purpose of the circle of willis
ensures an uninterrupted blood supply to the brain
blood flows to the kidneysthrough the ___
blood flows out of the kidneysthrough the ___
renal arteries
renal veins
nephron function
filter blood
what is the myogenic response?
the contraction of a blood vessel that occurs when intravascular pressure is elevated and, conversely, the vasodilation that follows a reduction in pressure
what is the tubuloglomerular feedback (kidneys)?
(watch a video too)
specialized cells in the nephron loop monitor the sodium concentration in the tubular fluid, which then signals the afferent arteriole to adjust its diameter to maintain a consistent glomerular filtration rate
primary functions of the kidney x2
osmoregulation: regulating the amounts of water and salts in the blood
excretion: the removal of metabolic waste products from the body
kidney structure x6 components & functions
renal artery brings blood to be filtered to the kidney (away from heart)
renal vein takes the filtered blood away from the kidney (back to heart)
ureter transports urine from the kidney to the bladder
renal pelvis is where urine is funneled before leaving the kidney through the ureter
medulla is the inner part of the kidney that regulates urine concentration
cortex is the outer layer of the kidney, where filtering and reabsorbing of essential substances occurs
osmolarity unit
milliosmoles per liter (mOsm/L)
what does urea result from?
waste product of protein oxidation
kidney nephron structure & function x6
glomerulus: filters small solutes from the blood
proximal convoluted tubule: reabsorbs ions, water & nutrients, also removes toxins and adjusts filtrate pH
descending loop of henle: aquaporins allow water to pass from filtrate into interstitial fluid
ascending loop of henle: reabsorbs Na+ and Cl- from filtrate into interstitial fluid
distal tubule: selectively secretes and absorbs different ions to maintain blood pH & electrolyte balance
collecting duct: reabsorbs solutes and water from filtrate
kidney nephron functions x4
ultrafiltration of blood
selective reabsorption of essential substances
secretion of waste products into filtrate to leave as urine
osmoregulation to create highly concentrated urine
define ultrafiltration
the process by which small molecules are filtered from the blood to enter the nephron, whereas larger molecules are held back and remain in the blood
where does ultrafiltration occur?
in the kidney nephron at the glomerulus and bowman’s capsule
what is filtrate?
the fluid that is filtered out of the blood and into the nephron
adaptations of the glomerulus for ultrafiltration? x2
high blood pressure to push small molecules out of the blood through the capillary walls and into bowman’s capsule
wider & more numerous fenestrations to allow more small molecules to pass into bowman’s capsule
why does the glomerulus have such high pressure?
due to a difference in diameter between the afferent arteriole (which carries blood into the glomerulus) and the efferent arteriole (which carries blood out of the glomerulus)
(narrowing of the diameter of the efferent arteriole results in a build-up of pressure within the glomerular capillaries)
what are fenestrations? what do they allow?
small openings in the capillaries of the kidneys, small intestine, and endocrine glands
allow molecules to pass between the blood vessel and surrounding tissues
what is bowman’s capsule?
a cup-shaped structure that wraps around the capillaries of the glomerulus
it is the first part of the nephron
where does filtrate go after being captured by bowman’s capsule?
flows into the proximal convoluted tubule for further processing
look at slide 90 and 91 d3.3
-
define lumen
the interior of the proximal convoluted tube, where the filtrate flows
the cells that line the lumen are specialized for the function of reabsorption and secretion. how is this seen? x4 ways
microvilli on the surface facing the tubule lumen increases the surface area for reabsorption of substances like glucose, amino acids, and ions
numerous mitochondria to provide ATP for active transport mechanisms involved in reabsorption
cells are connected by tight junctions to prevent leakage from the tubule lumen
a large number of channels and pumps for transport of materials across the plasma membrane
define selective reabsorption
the process by which specific molecules in the filtrate that were filtered out of the blood during ultrafiltration are actively transported back into the bloodstream
selective reabsorption occurs in the ______ at the ____________, which receives the filtrate from _________
kidney nephron
proximal convoluted tubule
bowman’s capsule
mechanisms by which substances move across proximal convoluted tubule cell membranes for reabsorption include: x5 ways & examples
Osmosis: Water follows the hypertonic concentration gradient established by the pumping of Na+ ions
Diffusion: Urea moves passively down its concentration gradient.
Facilitated diffusion: Cl- ions move passively through channel proteins
Active transport: Na+ ions are moved through pump proteins
Indirect active transport: Glucose and amino acids are moves through co-transporters that simultaneously move Na+ ions, utilizing the existing sodium gradient established by the Na+/K+ pump.
define secretion (in relation to blood & prox conv tubule)
when substances are actively transported from the blood into the proximal convoluted tubule
benefits of secreting things into filtrate x4
Excretion of metabolic waste products: secretion helps to remove waste molecules that were not filtered out by the glomerulus, such as bile salts, creatinine and urea.
Regulation of ion balance: secretion of additional ions helps to maintain the body’s electrolyte balance.
Removal of toxins: secretion can eliminate harmful substances from the blood, such as antibiotics, drug metabolites and heavy metals.
Acid-base balance: Secretion of hydrogen ions contributes to the regulation of blood pH for homeostasis
loop of henle ascending vs descending function
descending ⬇ limb: water drawn out
ascending ⬆ limb actively pumps sodium and chloride ions out (into the interstitial fluid) (this creates a concentration gradient that further draws water out in the descending limb)
define interstitial fluid
the fluid that surrounds cells in a tissue
the cortex is the outer layer of the kidney, what parts of the nephron does it include? x3
glomeruli
proximal convoluted tubule
distal convoluted tubule
the medulla is the inner layer of the kidney, what parts of the nephron does it include? x2
loops of henle
collecting ducts
what is the osmolarity of the interstitial fluid relative to the filtrate? (isotonic, hypertonic, hypotonic)
hypertonic due to the pumping of Na+ and Cl- out of the filtrate and into the interstitial fluid by cells of the ascending limb of the loop of henle
what is plasma osmolality a measure of
the concentration of solutes in plasma, which is the fluid part of blood
osmoregulation is a negative feedback loop that regulates the body’s water balance. what is this feedback loop upon heavy water intake?
heavy intake of water (hyperhydration)
⇩
high water content in blood plasma
(low osmolarity)
⇩
sensed by osmoreceptor cells in hypothalamus
⇩
pituitary gland releases less ADH
⇩
less water reabsorbed by kidney collecting duct
⇩
large volume of dilute urine goes to bladder
⇩
water content in blood plasma drops
(raising osmolarity)
low blood osmolality = ?
high blood osmolality = ?
low = hyperhydration (too much water in the blood plasma)
high = dehydration (not enough water in the blood plasma)
how do osmoreceptors work? x5 steps
have aquaporin proteins spanning through their plasma membranes through which water can diffuse
if plasma osmolarity becomes hypertonic, then water will move out of the cell due to osmosis, causing the osmoreceptor cell to shrink in size
when the cell shrinks in size, gated ions channels open and allow positively charged ions, such as Na+, to enter the cell
this causes initial depolarization of the osmoreceptor leading to action potentials being generated
these action potentials release of ADH from the posterior pituitary gland, which reaches target cells in the kidney collecting duct
what does ADH stand for?
antidiuretic hormone
to increase osmolality of blood, ____ will not be ______ by the cells of the collecting duct
water
reabsorbed
when blood plasma osmolality is high (dehydration), antidiuretic hormone (ADH) is released from the pituitary gland in the brain.
what does ADH do to lower osmolality?
causes cells of the kidney collecting duct to move vesicles storing aquaporin channels to the plasma membrane
vesicles then fuse with the the plasma membrane of the collecting duct cells, inserting the aquaporin channels into the membrane
water will then move through osmosis through the aquaporin channel, out of the filtrate and back into the blood plasma. the adding of the water to the blood plasma will decrease the blood osmolality.
