Renal System

A&P Exam 4

Direct functions of the kidneys

Regulation of water, inorganic ion balance, acid-base balance

Removal of metabolic waste and foreign chemicals from blood and excreting it in urine

Gluconeogenesis

Hormone production

Define gluconeogenesis

The creation of new glucose from non-glucose substrates

Where does urea and uric acid come from

Byproducts of protein breakdown

Where does bilirubin come from

Hemoglobin, a byproduct of breakdown of heme pigment and produces color derivatives

What hormones/enzymes do the kidneys produce? Explain

Erythropoietin - controls erythrocyte production

Renin - controls formation of angiotensin, which influences blood pressure and sodium balance

Vitamin D - activates it to influence calcium balance

Functional unit of kidney

Nephron

Name these structures

1. Renal artery

2. Renal vein

3. Renal pelvis

4. Ureter

5. Cortex

6. Medulla

7. Papilla

8. Capsule

9. Calyx

Describe the path of blood as it enters and leaves the kidney

Blood comes in from renal artery → dumped off in cortex (filtered) → filtrate moves through medulla in renal pyramids (modified) → dumped into calyx (drainage) → merges at renal pelvis (urine is removed) → clean blood is returned to systemic circulation via renal vein, urine sent to urinary bladder

Name the tubular components of nephron

A. Bowman’s capsule

B. Proximal convoluted tubule

C. Loop of Henle

D. Distal convoluted tubule

E. Collecting duct

Name the vascular components of nephron

A. Renal artery

B. Afferent arteriole

C. Glomerular capillaries

D. Efferent arteriole

E. Peritubular capillaries

F. Renal vein

Name and describe the two types of nephrons

Juxtamedullary (15%) - has long loops of Henle that dip in the medulla, closest to medulla, generates gradient in medulla for H2O reabsorption, peritubular capillaries are called vasa recta

Cortical (85%) - short loops of Henle, don’t contribute to gradient in medulla

Describe the renal cortex

Outer layer that contains…

• Renal corpuscles of nephrons

• Proximal and distal tubules of all nephrons

• Cortical nephrons

Describe the renal medulla

Inner layer (renal pyramids) that contains…

• Long loops of henle from juxtamedullary nephrons

  • Medullary portion of collecting ducts

Define the juxtaglomerular apparaturs

Specialized region that regulates glomerular filtration rate (GFR) and systemic blood pressure by sensing the amount of NaCl in filtrate

Controls release of renin

List parts of the juxtoglomerular apparatus

Juxtaglomerular cells, macula dense, sympathetic nerve fiber

Explain juxtaglomerular cells

AKA granular cells

Surrounds afferent arterioles

Synthesizes, stores, and secretes renin in response to BP, norepeinephrine, and macula densea

Explain the macula densa

Part of the wall of distal tubule

Senses filtrate flow and sends paracrine signals to afferent arteriole to regulate BP and amount of filtrate produced

Explain the sympathetic nerve fiber

Comes from the VM center, constricts afferent arteriole

Causes renin secretion from JG cells

___% of plasma is filtered; ___% continues into efferent arteriole

20; 80

Excretion formula

= filtered + secreted - reabsorbed

Examples of substances that are all freely filtered but 100% secreted, partially reabsorbed, and 100% reabsorbed

100% secreted - drugs, toxins

Partially reabsorbed - Na+, Cl-, water

100% reabsorbed - glucose, amino acids

Name the three basic renal processes

Glomerular filtration, tubular reabsorption, tubular secretion

Define glomerular filtration

The first step in urine formation where water and small dissolved substances are filtered out of the blood and into Bowman’s capsule, occuring in the glomerulus

What occurs in glomerular filtration

Blood enters glomerulus where afferent arteriole has high pressure → pushes fluid out of blood through a filtration membrane → filtrate enters Bowman’s capsule → leaves to enter proximal tubule

Describe the three layers composing the filtration barrier

Capillary endothelium (fenestrated for more exchange)

Basement membrane (negatively charged matrix)

Bowman’s epithelium (podocytes and filtration slits)

What substances cannot pass the filtration barrier and why

RBCs and plasma proteins because they’re too big to pass through the capillary fenestrations

Small proteins because they are negatively charged and will be repelled by the basement membrane

Explain starling forces involved in glomerular filtration

PGC (usually 60mmHg) - filtrates from glomerular capillary to Bowman’s space

PBS - opposes filtration

πGC - opposes filtration, determined by plasma proteins but usually deosn’t exist

How do renal arterioles regulate PGC

Decreased GFR

• Constricting afferent arteriole

• Dilating efferent arteriole

Increased GFR

• Constricting efferent arteriole

• Dilated afferent arteriole

Net glomerular filtration pressure equation

= PGC - PBS - πGC

Filtered load equation

= GFR x [Ps] (plasma solute)

Excreted load equation

= V (urine flow rate) x [Us] (urine solute)

If FL > EL, there’s net ____. If FL<EL, there’s net ____

Reabsorption, secretion

What % of filtered volume is reabsorbed in tubular reabsorption

99

What are the modes of tubular reabsorption

Diffusion and mediated transport

What are the two routes of tubular reabsorption

Transcellular transport - apical/luminal membrane → basolateral membrane → renal ISF → peritubular capillaries

Paracellular transport - tight junctions → renal ISF → peritubular capillaries

Explain the glucose concentration vs filtered load, reabsorption, excretion graph

Filtered load is normal, reabsorption keeps up with filtration at low plasma solute concentrations

Solute in urine with high plasma concentration will reabsorb but reach a transport maximum

Explain tubular secretion

Usually involves active transport but diffusion can occur

Occurs in proximal tubules

Also reaches a transport maximum

Define renal plasma clearance

The volume of plasma cleared of substance per unit time. Higher RPC means the kidneys are removing more of that substance from the plasma

What does RPC tell us?

= GFR - everything filtered is secreted (ex. insulin)

< GFR - clearance is close to 0 mL, partially reabsorbed substances are filtered

> GFR - active secreted into tubule, almost everything is filtered

What muscles are involved in micturition. What’s their type and activity during filling and micturition

Detrusor - parasympathetic - inhibited - stimulated

Internal urethral sphincter - sympathetic - stimulated - inhibited

External urethral sphincter - somatic motor - stimulated inhibited

What are two main points about total-body balance of water

For homeostasis to be maintained, intake must equal output

Urine is the main regulator for intake to match output

What are the proportions of total-body fluid

NaCl prop ECF volume prop MAP