Anatomy and Physiology Chapter 26 - Kidney Introduction, Kidney Nephron and Collecting Duct, and Renal Corpuscle Exchange

3 functions of the kidney and are what?

1. filter blood and make urine

2. regulate water, pH, and blood pressure

3. produce EPO and renin

retroperitoneal

10 structures of the kidney

1. capsule

2. renal cortex

3. renal medulla

4. major calyx

5. minor calyx

6. papilla of pyramid

7. renal pyramid

8. renal column

9. renal pelvis

10. ureter

the flow of blood in the kidneys

arteries:

1. renal

2. segmental

3. interlobal

4. arcuate

5. cortical radiate

6. afferent arterioles

7. glomerulus

8. efferent arteriole

9. peritubular capillaries

veins:

1. venules

2. cortical radiate

3. arcuate

4. interlobal

5. renal

3 compounds produced by the body that the kidneys get rid of

1. urea: mostly AA breakdown and is the most abundant

2. creatinine: generated from skeletal muscle via creatine phosphate breakdown

3. uric acid: formed from recycling RNA nitrogenous base (don’t want to lose too much carbon)

nephron

functional unit of the kidney that is highly organized, looped ducts that are sites of absorption and secretion

cortical vs. juxtamedullary nephrons

cortical: doesn’t extend into medulla and is ~80%

juxtamedullary: extend deep into the medulla, most important for water absorption and is ~20%

3 functions of the nephron

1. filtration: fluid moves from blood into capsular space (starts at glomerulus)

2. reabsorption: substances move from tubule fluid to blood

   1. transcellular route: solute enters apical membrane of tubule cells, travels through cytosol of tubule cells, exits basolateral membrane of tubule cells, and enters blood via endothelium of peritubular capillaries

   2. paracellular route: between tubule cells

3. secretion: substances move from blood to tubular fluid (urea, uric acid, creatine, H+, and K+)

   1. drugs and metabolies are sometimes stuck to plasma proteins (secreted in PCT)

   2. eliminate unwanted substances that were reabsorbed (urea and uric acid)

2 main components of the nephron

1. renal corpuscle

2. renal tubules

renal corpuscle and its components

found in the cortex and used for filtration

• glomerulus: made of simple squamous epithelium

  • intraglomerular mesangial cells: contractile cells that support, filtrate, and perform phagocytosis

• Bowman’s capsule:

  • outer layer

  • capsular space: fluid from blood enters into the nephron to get reabsorbed and secreted along nephron

  • visceral layer with podocytes: forms part of the filtration membrane

3 components of the filtration membrane

1. glomerular epithelium: has fenestrated capillaries

2. basement membrane

3. filtration slits of podocytes

8 molecules that get through the filtration membrane and 2 molecules that remain

pass through:

• water

• glucose

• AAs

• ions

• urea

• vitamins

• ketones

• little bits of proteins (albumin)

remain:

• formed elements

• most proteins (for blood osmotic pressure)

renal tubule and its 3 parts

found in the medulla and helps with absorption and secretion

1. proximal convoluted tubule (PCT)

2. nephron loop (loop of Henle)

3. distal convoluted tubule (DCT)

6 things about the proximal convoluted tubule (PCT)

• connects to the corpuscle and made of simple cuboidal epi. cells with microvilli

• secretes H+, NH4+, creatine, drugs, and toxins

• 60-70% filtrate reabsorbed

• facilitated transport and cotransport (glucose and AAs)

• active transport ions (Na+, Na/Kase, cotransport with HCO3-)

• osmosis

5 things about the nephron loop (loop of Henle)

• connects PCT and DCT

• reabsorbs ~50% water, 66% Na+ and Cl- remaining

• descending freely permeable to water; ascending impermeable to water

• ALT permeable to Na+; TAL actively reabsorbing Na+ and Cl-

• positive feedback: loose water, more solutes, greater solute reabsorbed

5 things about the distal convoluted tubule (DCT)

• leads to collecting system and is simple cuboidal epi. with few microvilli

• reabsorb Na+ and Cl- (cotransport); regulated by aldosterone (counter-transport)

• Ca2+ reabsorbed via calcitriol

• secretion of K+ and H+ due to counter-transport, acids, drugs, and toxins

• selective water reabsorption based on ADH

7 things about the collecting system

• many nephron DCTs drain into 1

• adjusts fluid’s composition and determines final osmotic concentration and urine volume

• aldosterone and ADH control

• Ca2+ reabsorbed via calcitriol

• reabsorption based on ADH

• intercalated cells to regulate acid-base balance

• principal cells that reabsorb water and secrete K+

osmotic concentration (osmolarity)

• the concentration of all dissolved “osmolytes” (solutes) in solution

• includes ions (Na+, H+, etc.) and other dissolved molecules like AAs

• hyperosmotic vs. hypoosmotic

3 filtration pressures

1. hydrostatic pressure

   1. glomerular hydrostatic pressure (GHP): needs high pressure than typical capillaries (afferent arteriole diameter smaller)

   2. capsular hydrostatic pressure (CsHP): opposes GHP due to resistance flow through PCT and goes into blood

   3. net hydrostatic pressure (NHP): GHP - CsHP

2. blood colloid osmotic pressure (BCOP): pressure due to materials in solution (proteins); none opposing inside capsule, so water moves into blood

3. net filtration pressure (NFP): NHP - BCOP = 10 mmHg

glomerular filtration rate and 4 controls to it

volume of filtrate formed each minutes by all glomeruli of the kidneys

1. NFP

   1. increase NFP must increase flow into glomerulus (vasodilation of afferent arteriole)

   2. decrease NFP must decrease blood flow

2. GHP: determined by BP

3. BCOP: depends on proteins in blood

4. CsHP