Chapter 16 - Homeostasis Flashcards
What is homeostasis?
Maintaining a constant internal environment
Why is homeostasis so important for enzymes?
Enzymes are sensitive to changes in pH and temperature
How are cells protected from changes in the external environment?
The conditions of the tissue fluid are carefully maintained
Why is homeostasis important in terms of water potential?
Water enters/leaves by osmosis, causing cells to swell/shrink
Why is it advantageous that an organism can regulate its internal environment?
It makes the organism more independent
What is the optimum point?
The point at which the system operates best
What is the function of the receptor?
Detects deviation from the optimum point
What is the coordinator?
Coordinates information from receptors to create the correct response
What is an effector?
Restores optimum conditions
What is negative feedback?
The stimulus detected by the receptor turns the system off
What is positive feedback?
Deviation from the optimum causes changes that result in greater deviation
What is the negative feedback system we study in detail?
The glucagon-insulin system
Describe the release of glucagon as a negative feedback system
Receptors detect a fall in glucose concentration. Glucagon is secreted, which causes the liver cells to convert glycogen to glucose and release it into the blood. The receptors then detect this rise in blood glucose concentration and stop releasing glucagon
Why is it advantageous to have two separate negative feedback systems controlling blood glucose concentration?
Gives the organism more control and independence
How do hormones reach the target cells?
Secreted from glands into the blood
Travels in blood plasma to target cells
What effectiveness do hormones have?
They are effective in low concentrations and have long-lasting and widespread effects
Describe the secondary messenger model
Adrenaline binds to a protein receptor on the cell membrane of a liver cell
This causes the protein to change shape inside the membrane
This activates the enzyme adenyl cyclase, which converts ATP to cAMP
The cAMP acts as the second messenger and binds to kinase, activating it
Kinase catalyses the breakdown of glycogen into glucose
What do the alpha cells secrete?
Glucagon
What do the beta cells secrete?
Insulin
What is glycogenesis?
Converting glucose - glycogen
What is glycogenolysis?
Breaking down glycogen to glucose
What is gluconeogenesis?
Producing glucose from sources other than carbohydrates
Why must the blood glucose concentration remain constant?
If it’s too low, there isn’t enough glucose for respiration
If it’s too high, it interferes with the water potential and water moves out of cells by osmosis
What are the three main sources of glucose?
Carbohydrates from the diet, glycogenolysis, gluconeogenesis
How does insulin lower the blood glucose concentration?
It changes the tertiary structure of the carriers, allowing more glucose into the cell by facilitated diffusion
Increases the number of glucose carrier proteins
Activates enzymes to convert glucose to glycogen and fat
Which cells don’t have receptors on their cell surface membranes?
Red blood cells
How is blood glucose concentration reduced?
Increasing the rate of absorption of glucose into cells
Increasing the respiratory rate of cells
Increased glycogenesis
Increased conversion of glucose to fat
How does glucagon increase blood glucose concentration?
Attaching to receptors on liver cells
Activating enzymes to convert glycogen to glucose
Gluconeogenesis
How does adrenaline increase blood glucose concentration?
Attaches to receptors on target cells
Activating enzymes to break glycogen down into glucose
What is type 1 diabetes?
The body is unable to produce insulin because the beta cells in the islets of Langerhans are attacked by the immune system
What is type 2 diabetes?
Glycoprotein receptors lose their responsiveness to insulin
Why does type 1 diabetes occur?
Genetics
Why does type 2 diabetes occur?
Lifestyle choices
How is type 1 diabetes controlled?
Insulin injections
How is type 2 diabetes controlled?
Lifestyle changes
How does the water potential of the body decrease?
Too little water is drank
Too much sweating
Lots of ions taken in
How does the body respond to a decrease in water potential?
Osmoreceptors in the hypothalamus detect the fall
ADH is released by the pituitary gland and secreted into capillaries
ADH passes to the kidney
ADH increases the permeability of the convoluted tubule and collecting duct to water
Receptors on the cell membrane bind to the ADH, activating phosphorylase
This causes vesicles to bind to the cell membrane, forming aquaporins
ADH increases the permeability of the membrane to urea, so the water potential of the fluid around the duct is even lower
Water leaves the collecting duct by osmosis
The osmoreceptors detect this change
The pituitary gland stops releasing ADH
How does the body respond to a rise in water potential?
The osmoreceptors detect the rise in water potential
Less ADH is released from the pituitary gland
The collecting ducts and tubules are less permeable
A larger volume of dilute urine is produced
What are the two things you must mention when describing urine?
Volume and concentration
Function of the fibrous capsule
Protects the kidney
Function of the cortex
An outer region made of Bowman’s capsules and convoluted tubules
Description of the medulla
Made of loops of Henle and collecting ducts
Function of the renal pelvis
Collects urine into the ureter
Function of the ureter
Carries urine to the bladder
Description of Bowman’s capsule
Surrounds the glomerulus. Contains podocytes
Description of proximal convoluted tubule
Loops surrounded by capillaries
Description of the Loop of Henle
A long loop surrounded by capillaries
Description of distal convoluted tubule
Another series of loops surrounded by capillaries
What is the afferent arteriole?
A small blood vessel that supplies the nephron with blood
What is the glomerulus?
A know of capillaries from which fluid is forced out
What is the efferent arteriole?
Carries blood away from the glomerulus. Has a smaller diameter than the afferent arteriole
What are the blood capillaries?
Surrounded the convoluted tubules, the loop of Henle. It is from the capillaries that these structures reabsorb salts, glucose and water
Describe the process of ultrafiltration
The afferent arteriole has a larger diameter than the efferent arteriole. This creates high hydrostatic pressure in the glomerulus which forces water, glucose and ions out to form a filtrate
How do podocytes allow the filtrate to leave the cell?
They have spaces between them that allow the filtrate to pass through
How does the endothelium allow the filtrate to leave?
It has spall gaps in that the fluid can pass through
What adaptations does the proximal convoluted tubule have that facilitates reabsorption?
Microvilli for a larger surface area
Lots of mitochondria for active transport
Infoldings for a larger surface area
Describe the process of reabsorption in the proximal convoluted tubule
Sodium ions are transported out of the convoluted tubule into the blood by active transport. This results in a lower concentration of Na+ ions in the tubule
Na+ ions diffuse down a concentration gradient from the lumen of the tubule into the epithelial cell by facilitated diffusion
The carrier proteins each allow another molecule through with the sodium ions (co-transport)
These molecules then diffuse into the blood
How does the loop of Henle maintain a sodium ion concentration gradient?
Na+ ions are actively transported out of the ascending limb using ATP
This creates a low water potential in the interstitial space between limbs
Because the walls of the ascending limb are impermeable to water, water doesn’t leave them by osmosis like normal
Water moves out of the descending limb by osmosis
The filtrate loses water as it moves down the descending limb
At the bottom of the ascending limb, Na+ ions move out by diffusion and active transport
Between the ascending limb and the collecting duct, there is an increasing concentration of ions as you go further into the medulla
The collecting duct is permeable to water so water passes out of it by osmosis into blood vessels
The water potential of both the filtrate and the interstitial space is lowered, so water moves out of the collecting duct through aquaporins by osmosis
The counter-current multiplier ensures there is always a concentration gradient
Characteristics of the descending limb of the loop of Henle
Narrow with thin walls that are permeable to water
Characteristics of the ascending limb of the loop of Henle
Wider walls that are impermeable to water
What is the main function of the distal convoluted tubule?
Many mitochondria and a high surface area allow the tubule to reabsorb material from the filtrate by active transport. The permeability of the membrane alters to make the final changes to the amount of water and salts that are reabsorbed
