Homeostasis and the Kidney Flashcards
(57 cards)
What is homeostasis?
The maintenance of constant internal conditions, controlled by the endocrine system.
Why is it useful to keep the concentration of body fluids at a constant and optimum level?
To protect cells from changes in the external environment, ensuring reactions continue at a constant and appropriate rate.
What is negative feedback?
Describes systems which reverse a change from a normal value.
Describe the series of steps of negative feedback
- The set point for a factor is the norm at which the system operates.
- A receptor detects the level of the factor and its deviation from the set point
- The receptor sends instructions to a co-ordinator or controller
- The co-ordinator communicates with one or more effectors which make responses that are corrective
- The factor returns to normal, monitored by the receptor and information is fed back to the corrector, which stops making the correction
What are the two main functions of the kidney?
Excretion- the removal of nitrogenous metabolic waste from the body.
Osmoregulation- the control of the water potential of the body’s fluids, such as plasma, tissue fluid and lymph, by the regulation of the water content in the body.
What happens to surplus amino acids in the body?
They are deaminated in the liver and the amino group is converted to ammonia, then to less toxic urea. The urea is carried in the plasma to the kidneys and excreted in urine.
Describe the structure of the kidney
A renal capsule covers each kidney. Each receives blood from a renal artery and returns blood through a renal vein. The blood from the renal artery is filtered in the cortex at the Bowman’s capsules. The medulla contains the long loop of Henle and the collecting ducts that carry urine to the renal pelvis. The pelvis empties urine into the ureter which carries it to the bladder.
What is a neprhon?
The functional unit within the kidney. There are one million in each.
Describe blood flow through the neprhon
An afferent arteriole brings blood to the nephron and divides into 50 parallel capillaries in the glomerulus. From there, the filtered blood is carried by an efferent arteriole to either a capillary network surrounding the proximal and distal convoluted tubules or the vasa recta, a capillary network surrounding the loop of Henle. The blood filtrate is diverted through the nephron and the collecting ducts of many nephrons join to carry urine to the pelvis and ureter.
Why does blood arriving in the glomerulus from the afferent arteriole have high pressure?
-The afferent arteriole has a wider diameter than the efferent arteriole
-The hearts contraction increases the pressure of arterial blood
What are the three layers separating the blood entering the glomerulus from the Bowman’s space?
-The wall of the capillary, which is a single layer of endothelium cells with pores called fenestrations.
-The basement membrane, an extra-cellular layer of proteins acting as a molecular filter between the capillary wall and the nephron.
-The wall of the Bowman’s capsule, made of squamous epithelial cells called podocytes
What is ultrafiltration?
Filtration under high pressure
Describe the ultrafiltration of blood in the glomerulus
The high pressure in the capillaries of the glomerulus forces water, glucose, salts, urea and amino acids through the fenestrations of the capillaries, the basement membrane and slits between pedicels into the Bowman’s capsule. Blood cells, platelets and large proteins remain in the blood as they are too large to pass through.
What is selective reabsorption?
The process by which useful products are reabsorbed back into to the blood, as the filtrate flows through the nephron.
Describe the adaptations of the proximal convoluted tubule for selective reabsorption
-Large surface area, as it is long and there are a million nephrons in each kidney
-Cuboidal epithelial cell walls, with their surface area increased by microvilli
-Contains many mitochondria, providing ATP for active transport
-Has a close association with capillaries and tight junctions between the cells.
How are glucose and amino acids reabsorbed back into the blood?
By co-transport with Na+ ions. The glucose or amino acid and two Na+ ions bind to a transporter proteins and enter the cell by facilitated diffusion, dissociate from the transporter and diffuse across.
How is water reabsorbed back into the blood?
By osmosis, passively, as the reabsorbed ions lower the water potential of the blood.
How is half the urea and small proteins reabsorbed back into the blood?
By diffusion, down a steep concentration gradient.
What is the filtrate isotonic to at the base of the proximal convoluted tubule?
The filtrate is isotonic with the blood plasma, as it has lost salts, water, urea, glucose and amino acids.
Why might the concentration of glucose in the body be high, causing it to be lost in the urine?
-The pancreas secretes too little insulin (type I diabetes)
-The response of liver cells to insulin is reduced because insulin receptors in surface membranes are damaged (type II or gestational diabetes)
Why do the distal convoluted tubule and collecting duct operate the fine control of the body’s water control?
As they can reabsorb varying volumes of water in response to the body’s needs.
How are the walls of the ascending limb of the loop of Henle adapted?
They are impermeable to water and actively transport Na+ and Cl- ions out of the filtrate in the tubule into the tissue fluid in the medulla.
How are the walls of the descending limb of the loop of Henle adapted?
They are permeable to water, and slightly permeable to Na+ and Cl- ions.
Describe the passage of filtrate up the ascending limb of loop of Henle
The loops collectively concentrate salts in the tissue fluid, which has a lower water potential. As the filtrate travels up the bend in contains less and less ions, becomes increasingly dilute and its water potential increases.
