Chapter 16 Flashcards
How is the urinary system closely associated with the reproductive system
- Shared embryonic development
- together termed urogenital system
What are the 6 principle organs of the urinary system
2 kidneys, 2 ureters, bladder and urethra
What are the functions of the kidneys?
1) Filter blood, separate wastes and excrete them, and return useful material to the bloodstream.
2) regulate blood volume and pressure by eliminating or conserving water as necessary
3) Regulate the osmolarity of body fluids by controlling the relative amounts of water and solutes eliminated.
4) Secrete enzyme “renin” which activates hormonal mechanisms that control blood pressure and electrolyte balance
5) Secrete hormone “erythropoietin” which stimulates the production o red blood cells and thus supports the oxygen-carrying capacity of the blood
6) Carry out the final step in synthesizing hormone “Calcitriol” and thereby contributing to calcium homeostasis
7) Detoxify some drugs
What is Excretion?
Process of separating wastes from body fluids and eliminating them
What is “waste”?
Any substance that is useless or present in excess of the body’s needs
What is a Metabolic Waste?
Waste substance produced by the body
e.g. a by-product of ATP production or protein catabolism
What other systems besides the urinary system excrete wastes?
- Respiratory excretes CO2
- Digestive and Integumentary system excretes water and salts
What are some Nitrogenous wastes?
- Urea –> makes up 50%; converted from ammonia in the liver, carried in blood plasma to kidneys, filtered into urine and excreted
- Uric Acid –> Produced by catabolism of nucleic acids
- Creatine –> Produced by catabolism of creatine phosphate.
What are the 4 stages of Urine formation?
1) Glomerular Filtration –> Creates a plasma-like filtrate of the blood
2) Tubular reabsorption –> Removes useful solutes from the tubular fluid and returns them to the blood
3) Tubular secretion –> Removes additional wastes from the blood, adds them to the tubular fluid.
4) Water Conservation –> Removes water from the urine and returns it to blood; concentrates wastes
What are the 3 layers of the filtration membrane?
1) Endothelium of the Capillary –> glomerulus with fenestrated capillaries; penetrated by large filtration pores; small enough to exclude RBC’s
2) Basement Membrane –> Mesh of Glycoproteins. Holds back most proteins
3) Filtration Slits –> Created by podocytes of capsule; bulbous cell bodies with several thick arms; arms with numerous extensions, “foot processes”; Wrap around capillaries and lace together
How much higher is blood pressure in the glomerular capillaries than in most other capillaries?
60 mm Hg
Which is bigger the afferent or efferent arteriole in the glomerular capillaries?
Afferent which results in increased blood pressure
What are the 2 forces that oppose blood pressure in glomerulus?
1) Fluid pressure in the capsular space
2) Osmotic pressure of the blood
What does higher blood pressure in the glomeruli do to the kidneys?
Makes them especially vulnerable to hypertension which can have devastating effects on renal function. Hypertension ruptures glomerular capillaries and leads to scarring of the kidneys (nephrosclerosis). It promotes atherosclerosis of the renal blood vessels and thus diminishes renal blood supply. Over time, Hypertension often leads to renal failure.
What is the GFR?
Glomerular Filtration Rate – the amount of filtrate formed per minute by 2 kidneys
What happens if the GFR is too high?
Fluid flows through the renal tubules too rapidly for them to reabsorb the usual amount of water and solutes. Urine output rises and creates a threat of dehydration and electrolyte depletion.
What happens if the GFR is too low?
Fluid flows sluggishly through the tubules and they reabsorb wastes that should be eliminated in the urine.
How is GFR regulated by hormonal chain reactions?
When Blood pressure drops, sympathetic nerves stimulate the kidneys to secrete enzyme “Renin” which converts Angiotensiongen (a blood plasma protein) into Angiotensin I. Angiotensin-converting enzyme converts this to Angiotensin II (a hormone that acts in several ways to restore fluid volume and blood pressure)
What are Some effects of Angiotensin II?
- Makes one thirsty and encourages water intake
- Stimulates adrenal cortex to secrete aldosterone which promotes retention of sodium and water.
- Stimulates Pituitary to secrete ADH which promotes water retention
- It is a Potent Vasoconstrictor meaning it constricts efferent more than afferent arteriole of nephron and sustains glomerular pressure when blood pressure is low.
What is Renal Autoregulation?
- Also known as local control, it refers to the ability of the nephrons to adjust their own blood flow and GFR even without external control
- Enables nephrons to maintain a relatively stable GFR in spite of changes in arterial blood pressure.
What are the 2 mechanisms of Autoregulation?
1) Myogenic Mechanism –> Smooth muscle has a tendency to contract when stretched. A rise in arterial blood pressure stretches the afferent arteriole. In response, the arteriole contracts and prevents blood flow into the glomerulus from changing much. When blood pressure falls, the afferent arteriole relaxes and allows blood to flow more easily into the glomerulus. GFR remains fairly stable.
2) Tubuloglomerular Feedback –> Involves communication between the glomerulus and renal tubule through a complex of structures called the juxtaglomerular apparatus.
What are the 2 special cell types which occur in the Juxtaglomerular apparatus?
1) Macula Densa Cells –> Epithelia cells at the end of nephron loop facing arterioles
2) Juxtaglomerular Cells (JG) –> Enlarged smooth cells located in afferent arteriole across from the macula. Dilate or constrict when stimulated by macula. Secrete Renin.
