Chapter 14 Homeostasis Essay QS Flashcards
Describe the principles of homeostasis. [6]
- maintenance of a constant/stable, internal environment/ set point/ optimal level
- increases stability / decreases disturbance
- despite changes in external environment
- involves negative feedback mechanisms
- ref. role of receptor / sensor / monitor
- to detect changes from set point / deviations
- coordination by nervous system
- and endocrine system / hormones
- effector / muscle / gland
- produces a response/ output/ restoration of, norm/ set point
Explain the source and importance of removing nitrogenous waste products from the body. [6]
- deamination
- ref. to ornithine cycle
- ref. to not all urea/produced each day/always some present
- ref. to urea
- ref. to creatinine & uric acid
- & ammonium ions
- produced in liver
- continuously/from excess amino acids
- toxic
- allowed to accumulate
- ref. to potential damage to tissues
Describe the structure of the kidney, including its associated blood vessels. [6]
- (outer) cortex
- medulla
- pelvis
- renal artery
- renal vein
- nephron/(kidney tubule)
- renal capsule/PCT/DCT, in cortex
- loop of Henle/collecting duct, in medulla
- glomerulus
- afferent & efferent arterioles
- capillary network around, PCT/loop/DCT
Discuss the role of the kidney in the control of water and metabolic wastes in the body. [10]
- osmoregulation/control of water content of body fluids/blood
- ultrafiltration of blood in glomerulus
- forming filtrate in Bowman’s capsule
- water & urea passed into filtrate
- reabsorbed (of water) in collecting duct
- determined by ADH
- produced when low blood water content
- increases permeability of walls of collecting duct/ increased water absorbed
- leaves tubule/collecting duct by diffusion/osmosis into tissues of medulla
- down water potential gradient created by NaCl
- & loop of Henle
- urea
- into blood vessels of vasa recta
- formation of small volume of concentrated urine/less water in urine
- water by osmosis to maintain blood pressure
Describe the process of ultrafiltration in the kidney/ explain how glomerular filtrate is formed. [8]
- endothelium of, blood capillaries/ glomerulus
- more/large, gaps between endothelial cells
- podocytes
- large gaps between podocytes/ filtration slits
- basement membrane, selective barrier/ acts as a filter
- prevents, large protein/RMM > 68 000, passing through
- no cells pass through
- named molecule which is filtered ; e.g. urea/water/glucose/uric acid/creatinine/ Na+/K+/Cl-
- high, blood/hydrostatic, pressure in glomerulus
- afferent arteriole wider than efferent arteriole
- lower pressure in, renal/Bowman’s, capsule
- fluid forced into capsule/ultrafiltration
Describe the mechanisms involved in reabsorption in the proximal convoluted tubule and describe how
the epithelial cells of the proximal convoluted tubule are adapted to carry out this process. (9)
mechanisms
- active transport
- Na+ out of pct cells / into blood
- (sets up) Na+ ion gradient
- facilitated diffusion
- using protein carrier
- cotransport (from lumen to pct cell)
- of, glucose / amino acids / ions
- osmosis
- down water potential gradient
- diffusion
- down a concentration gradient
adaptations
- microvilli ; A brush border
- many mitochondria ;
Describe the role played by ADH in osmoregulation in mammals. [7]
- low blood water content / water potential
- detected by osmoreceptors
- in hypothalamus
- ADH produced / released
- from posterior pituitary gland
- target kidney
- cells of collecting duct
- binds to receptors
- vesicles with water permeable channels
- fuse with cell membrane
- cells more permeable to water / water passes into cells
- urine lower volume
- higher concentration
Outline how the blood glucose concentration is regulated by insulin and glucagon. [8]
- glucagon from α cells
- insulin from β cells
- (binds to receptors on) target cells / liver / muscles
- ref. to vesicles containing glucose carrier proteins
- conversion of glucose to glycogen / glycogenesis
- increase (in rate of) uptake of glucose / permeability to glucose of cells
- increased fatty acid / fat synthesis / glucose to fat
- increased rate of oxidation / respiration of glucose
- glucagon raises blood glucose
- binds to receptors (on target cells / liver)
- conversion of glycogen to glucose / glycogenolysis
- conversion of amino acids to glucose
- ref. fats to glucose
Describe how adrenaline can stimulate liver cells to convert glycogen to glucose. [7]
1 adrenaline binds to receptor
2 on (cell surface) membrane of liver cells
3 activates / stimulates, G protein
4 activates / stimulates, adenyl(yl) cyclase
5 cyclic AMP made from ATP
6 (cAMP is) second(ary) messenger
7 (cAMP) activates / stimulates / binds to, kinase
8 initiates enzyme cascade
9 amplifies signal
10 (activates) glycogen phosphorylase
Describe the role of abscisic acid (ABA) in the closure of stomata during times of drought. [8]
- ABA is a stress hormone
- ABA, released/increases, during drought
in context of guard cell
3 ABA binds to its receptor on (cell surface) membrane
4 stops, H+ / H ions / protons, leaving (guard cell cytoplasm)
5 Ca2+ enters
6 Ca2+ is a second(ary) messenger
7 (Ca2+ / Cl-/ K+) channel (proteins) open ;
8 Cl– / anions, leave ;
9 K+ leave ;
10 water potential (in cell) increases
11 water leaves by osmosis ;
12 volume of, cell / vacuole, decreases ;
13 cell becomes flaccid closing, stoma / pore ;
Explain the mechanism by which guard cells open stomata. [9]
- proton pumps in cell surface membranes (of guard cells)
- pump H+ out (of cells)
- low(er) H+ conc inside (cell)
- inside of cell more negative (than outside)
- K+ channels open
- K+ move into (cell)
- by facilitated diffusion
- Cl - ions enter
- water potential of cell decreases
- water moves into cell, by osmosis / down a water potential gradient
- ref. to aquaporins
- volume of (guard) cells increases
- (guard) cells become turgid / increase in turgor pressure of (guard) cells
- ref. to unequal thickness of cell wall (of guard cell)
