Homeostasis Flashcards
Positive Feedback
A change or fluctuation triggers a response that results in an even greater deviation form the normal level
Negative Feedback
A response which returns internal environment to optimum when there are changes or fluctuations
Why Regulate Temperature?
To ensure stable rate of enzyme-controlled reactions. Prevent damage to membranes
High temperatures: enzymes denature
Low temp: insufficient kinetic energy for enzymes and substrates
Thermoregulation in Ectotherms
Exposing bodies to the Sun to warm up.
Gaining warmth from the ground.
Taking shelter or standing in shade to cool down.
Endotherms Thermoregulation: Gaining Heat
Vasoconstriction: diameter of arterioles near the skin made narrower so lower vol of blood reaches skin surface so less heat lost.
Shivering: involuntary rhythmic contractions
Raising Hairs: traps still air close to skin which insulates
Increased Metabolic Rate: more respiration so heat gain
Endotherms Thermoregulation: Cooling Down
Vasodilation: diameter of arterioles near the skin made wider so higher vol of blood reaches skin surface so more heat loss
More Sweating (or panting in furry animals): evaporation of water from skin (mouth and tongue) results in cooling
Lowering Body Hair
Why Regulate Blood Glucose Concentration?
Maintain constant blood water potential.
Maintain glucose concentration for respiration when needed
Factors that Affect Blood Glucose Concentration
Diet (consumption of carbohydrates)
Rate of Glycogenolysis
Rate of Gluconeogenesis
Insulin Action
Beta cells in islets of Langerhans in pancreas detect high blood glucose conc. and secrete insulin into blood
Insulin binds to specific surface receptors on target cells.
This increases the permeability of muscle and liver cells to glucose (increasing the number of glucose carrier proteins in the cell membrane and opening the carrier proteins by triggering a conformational change) so glucose is absorbed into the cells.
Insulin also activates enzymes for glycogenesis in these cells.
Insulin stimulates adipose tissue to convert glucose into fat
Methods of Lowering Blood Glucose Conc.
Glycogenesis: Conversion of glucose to glycogen in muscle and liver cells.
Increasing rate of absorption of glucose into cells
Increasing respiratory rate of cells, so more glucose is used up
Increasing conversion of glucose to fat
Glucagon Action
Alpha cells in islets of Langerhans in pancreas detect low blood glucose conc. and secrete glucagon into blood
Glucagon binds to specific surface receptors on target cells
This activates enzymes for glycogenolysis and gluconeogenesis
Increasing Blood Glucose Concentration
Glycogenolysis: hydrolysis of glycogen into glucose in the liver
Gluconeogenesis: conversion of amino acids and glycerol to glucose in the liver
Second Messenger Model
Adrenaline and Glucagon
Adrenaline binds to specific protein receptor on target cell.
Protein receptor changes shape inside the membrane.
This activates the enzyme adenyl cyclase which converts ATP to cAMP
cAMP (second messenger) binds to protein kinase enzyme, changing its shape and activating it.
Kinase enzyme catalyses glycogenolysis
Type 1 Diabetes
Type 2 Diabetes
Structure of Kidney
Fibrous capsule (outer membrane)
Cortex (lighter outer region with Bowman’s capsules and convoluted tubules)
Medulla (darker inner region with loops of Henle, collecting ducts and blood vessels)
Renal Artery
Renal Vein
Renal Pelvis (white cavity that collects urine into ureter
Ureter (tube carries urine to bladder)
Structure of Nephron
Renal Capsule (contains glomerulus, a mass of blood capillaries)
Proximal Convoluted Tubule
Loop of Henle
Distal Convoluted Tubule
Collecting Duct
Ultrafiltration in Glomerulus
Blood arrives to renal capsule through afferent arteriole and leaves through efferent arteriole
Afferent is much wider than efferent which creates hydrostatic pressure in the glomerulus.
Glucose, water and mineral ions pushed out of the blood capillaries through the basement membrane to form the glomerular filtrate in the proximal convoluted tubule.
Blood cells and proteins are too large to leave.
Basement Membrane
The endothelial cells of the capillaries in the glomerulus have pores which are large enough for glucose, water and mineral ions to be forced out but not proteins or blood cells.
The inner layer of the Renal capsule has podocytes (specialised cells) which has gaps to allow the filtrate to pass between and under them rather than through.
Selective Reabsorption in Proximal Convoluted Tubule
Na+ ions actively transported out of epithelial cells into blood. Creates conc. gradient for facilitated diffusion of Na+ ions from lumen of PCT into epithelial cells via co transporter proteins.
Glucose molecules diffuse into epithelial cells via cotransport with Na+ ions.
Glucose diffuses from epithelial cells into blood
All glucose is reabsorbed in PCT
Proximal Convoluted Tubule Adaptations
Epithelial cells have many mitochondria for active transport of Na+ ions
Microvilli to provide a large surface area for reabsorption via cotransporter proteins
Infoldings at base to provide a larger surface area for diffusion into blood
Loop of Henle
Ascending loop: Na+ ions actively transported out into the interstitial region. Ascending loop is impermeable to water.
Lower water potential in interstitial region and higher in descending loop, so water moves out of descending limb via osmosis and is reabsorbed.
Countercurrent multiplier as water potential gradient is maintained for full length of descending loop.
ADH
Osmoreceptors in hypothalamus detect fall in water potential.
Pituitary gland secretes ADH into blood where it travels to nephron
ADH binds to specific receptors on cell surface membrane off collecting duct and DCT.
This activates the enzyme phosphorylase which causes vesicles containing aquaporins to diffuse to cell surface membrane and fuse with it embedding the aquaporins
This increases the permeability of the DCT and collecting duct so more water is reabsorbed.
