3.7 Homeostasis And The Kidney Flashcards
What is homeostasis
Maintenance of a constant internal environment
Why is homeostasis so important
Cells can function efficiently, independently of the fluctuations in the conditions of the external environment
Some examples of homeostasis
Core body temperature
Glucose levels
Solute potential
How does negative feedback work
Corrects deviations from the set point
Examples of negative feedback
Insulin
Antidiuretic hormone
Sequence of events that go on for a negative/positive feedback to happen
Input is detected by a receptor which monitors the condition and provides input to the control centre which then evaluates information and provides output to an effector which will initiate a response designed to take away the deviation and restore the norm
How does positive feedback work
By enhancing the size of the stimulus
Examples of positive feedback
Oxytocin during childbirth
What parts of the nephron are in the cortex
Bowmans capsule
Proximal convoluted tubule
Distal convoluted tubule
What parts of the nephron are in the medulla
Descending limb
Loop of henle
Ascending limb
Collecting duct
Simply, what happens during ultrafiltration
Urea is removed from the blood as the glomerulus and Bowmans capsule work together to filter the blood under high pressure
How is there high pressure during ultrafiltration
The Blood supply to the glomerulus enters through the afferent arteriole and leaves through the efferent arteriol
The efferent is narrower than the afferent which increases the hydrostatic pressure of the blood plasma
3 part filter
• endothelium of capillaries of Glomerulus has fenestrations between the cells to increase filtration
• podocytes of Bowman’s Capsule have finger like projections called pedicels which wrap around the capillaries, the filtration slits between pedicels allow free passage of the filtrate from blood in the lumen of the Bowman’s capsule but not proteins and cells as they’re mostly too large
• basement membrane of capillaries and podocytes act as a selective barrier which allow water and small molecules to pass from the blood into the nephron
How is the efficiency of ultrafiltration increased
• pedicels increase surface area
• there is a short diffusion distance between podoctyes and the capillary
• filtration slits between pedicels increase the concentration gradient between the tissue fluid
What is the mechanism of ultrafiltration
• the large hydrostatic pressure causes small soluble molecules such as glucose, amino acids, salt, water and urea to be forced out of the plasma and they enter the channels between the pedicels and the capillary walls. The concentration then increases in the channels do they enter the Bowman’s capsule and form the glomerular filtrate
• the basement membrane of the capillary acts as a selective barrier between the blood and the nephron and allows small sized particles through whilst plasma proteins and cells remain in the blood due to their larger size
Net filtration pressure of ultrafiltration
The hydrostatic pressure is greater than the combined effect of the osmotic pressure of the plasma and fluid pressure of the filtrate so water and small molecules pass out of the plasma
What is osmoregulation
Control of the water content and solute composition of bodily fluids such as blood, tissue fluid and lymph
What is excretion
Elimination of waste products of metabolism from an organism
What biological molecule is used in excretion and why
Amino acids cannot be stored so excess amino acids are deaminated in the liver so the amino group forms ammonia which is converted to urea and transported into the blood plasma
Where does selective reabsorption occur
Proxima convoluted tubule