3.7 Homeostasis and the kidney Flashcards
What is the definition of homeostasis?
Mechanisms by which a constant internal environment is achieved
What are 3 factors controlled by homeostasis?
Temperature, blood glucose and water levels
What is negative feedback?
Increase causes a decrease in production and vis versa
What are the 3 stages in the negative feedback loop?
Detector, Controller and effector
What detects low water levels?
Osmoreceptors in the hypothalamus
What controls Water levels and how?
Posterior lobe of the pituitary gland release ADH
What effects the water levels of the blood?
The permeability of the walls of the collecting ducts
What are the 2 functions of the kidney?
excrete urea and control and regulate water and ion levels
What processes occur in the nephron?
Ultrafiltration, selective reabsorption, secretion
What structures are present in the nephron?
Bowman’s capsule, loop of Henle, distal convoluted tubes, collecting duct
What is urea?
Toxic waste product formed from deaminated amino acids
Where does ultra filtration occur?
The bowman’s capsule
What is the function of the Ureter?
Transport urine from the kidneys to the bladder
What is the medulla?
inner part of the kidney, contains loop of Henle
What is the cortex?
Outer part of the kidney, contains glomeruli and bowmans capsules
What are the adaptations for ultra filtration? (3)
Hydrostatic pressure (created by the narrowing from the afferent to efferent capillaries) Basement membrane of capillaries acts as a selective barrier, inner layer of podocytes allow movement of small molecules
What is ultrafiltration?
non selective filtering of small soluble molecules from the blood plasma
Where does selective reabsorption occur?
Proximal convoluted tubule
How is the PCT adapted for selective reabsorption?
Microvilli, tight junction (preventing seepage), capillaries maintain conc gradient, short diffusion pathway, abundant mitochondria (good ATP supply)
How are glucose and amino acids reabsorbed?
Secondary active transport using co-transport with sodium
How are mineral ions reabsorbed?
Active transport
How is water reabsorbed?
Osmosis
How are proteins reabsorbed?
diffusion
What is the glucose threshold?
reabsorption is limited by the number of proteins available for facilitated diffusion
What are the functions of the descending limb in the loop of Henle?
highly permeable to water
Na+ and Cl- ions enter via facilitated diffusion
What are the functions of the accending limb in the loop of Henle?
Impermeable to water
Pumps out Na+ and Cl- ions (first by facilitated diffusion then by active transport)
What is the function of the loop of Henle?
To create a low water potential in the medulla
What is secondary active transport?
Coupling of diffusion down a conc gradient providing energy for active transport
How is a sodium gradient created in the sodium potassium pump?
Na+ actively transported out of epithelial cells to intercellular space
Na+ concentration is reduced creating a gradient between the lumen of the nephron and the epithelial cytoplasm
How does Sodium enter the blood?
1 glucose molecules and 2 sodium ions bind to a transport protein in cuboidal epithelium
They are carried into the cell by facilitated diffusion
Na+ diffuses into the capillary
How does Glucose enter the blood?
Energy provided by sodium diffusion allows glucose to enter the blood by active transport
How do aquaporins work?
Bind to collecting duct osmoreceptors and incorporate via vesicles into the membrane
this creates pores allowing water molecules to pass thorough the membrane in single file down a gradient
What do aquatic animals excrete?
Ammonia
How do aquatic animals excrete waste?
ammonia dissolves and is dilulted and quickly diffuses across the gills
What do birds and insects excrete?
Uric acid
Why do birds and insects excrete uric acid?
low toxicity for infants in eggs
lightweight to aid flight
low water requirements to excrete (large energy cost)
What do mammals excrete?
Urea
Why do mammals excrete Urea?
Less toxic than ammonia
can be tolerated for short periods
What causes kidney failure? (5)
Diabetes
high blood pressure
auto immune disease
infection
crushing injuries
How does diabetes cause kidney failure?
high glucose levels scars the glomerulli
How does high blood pressure cause kidney failure?
damages the capillaries preventing ultra filtration
What are 5 treatments for kidney failure?
Dietary restrictions on salt and protines
Blood pressure drugs
Potassium and calcium level drugs
Dialysis
transplants
