A&P 3

Kidney function + how they do this (general overview)

homeostasis by regulating the volume + composition of the ECF (interstitial fluid)

• they do this by balancing the intake, production, excretion, and consumption of organic/inorganic compounds

Tasks that allow the kidneys to balance (6 + def)

1. Regulation of Blood - ionic composition + pH; the renal excretion of Na, K, Ca, Mg, H, and HCO3 balance the intake + excretion of these substances through other routes

2. Excretion of Organic Waste Products - ex: urea + creatinine + uric acid (↑↑ levels in blood = kidney failure)

3. Blood Pressure Regulation - a) by way of renin formation + release and b) by way of renal control of blood volume

4. Hormone Production - a) through formation + release of the hormones b) Erythropoietin which stimulates RBC production and c) Calcitriol, the active form of Vitamin D

5. Maintaining Blood Osmolarity - separately regulates loss of H2O and loss of solute

6. Regulation of Blood pH - involves balance of H+ and HCO3-

Kidney failure flow chart

Kidney failure → substances accumulating in the blood + ECF → change in body’s internal environment → ↓body cell function → death

Color + Location of Kidney (5)

• reddish brown

• positioned on upper posterior wall of the abdominal cavity (T₁₂ - L₃)

• each capped by adrenal gland (suprarenal gland)

• located in the retroperitoneal

• right kidney lower than left because the liver pushed the right kidney down

Hilum vs Renal Sinus

Hilum - indentation on the medial border through which most structures enter (ex: renal artery) or leave (ex: renal vein, ureter) the kidney

Renal Sinus - internal space the hilum opens into which contains the renal vessels + the renal pelvis + calyces

3 layers of tissue surrounding kidneys (+ def)

1. Renal Capsule - innermost layer, directly covers the kidney; fibrous

2. Adipose Capsule - mass of perirenal fat surrounding the renal capsule

3. Renal Fascia - surrounds the adipose capsule, completely enclosing + anchoring the kidney to the posterior abdominal wall

Internal regions/divisions of kidney (renal parenchyma)

Renal parenchyma is divisible into 2 regions (3 if you include renal pelvis)

• renal cortex

• renal medulla

Cortex layer/region (3 characteristics)

• deep to the renal capsule

• outer layer

• divides into “cortical zone” (outer) and “juxtamedullary zone” (inner)

Medulla layer (+ renal pyramids + renal lobe + papilla) (5)

• deep to the cortex

• formed by several triangular renal pyramids

Papilla = tip of renal pyramid

• renal pyramids point to the renal pelvis

Renal Lobe = 1 pyramid + overlying cortex + ½ each adjacent column

Collecting System (3)

Minor Calyces

• Each minor calyx is funnel shaped with a papilla projecting into it

Major Calyces

• Each major calyx is formed by the fusion of several minor calyces

Renal Pelvis

• formed by the fusion of the major calyces = the expanded upper part of the ureter

Nephron (def)

functional unites of the kidneys where urine is formed

• 1 million per kidney

Types of Nephrons (2)

Cortical nephrons

• 80-85% of the nephrons in the kidney

• have short loop of henle’s

Juxtamedullary nephrons

• corpuscles located at the junction of the cortex + medulla of the kidney

• have long loop of henle’s

• important in the counter-current system by which the kidneys concentrate urine

Each nephron consists of 2 parts:

The Glomerulus

• network of parallel capillaries

Renal Tubule

• epithelial lined tube with various regions that differ from one another anatomically (epithelial variations)

Epithelial Variation examples (5)

• Bowmans capsule

• Proximal convoluted tubule

• Distal convoluted tubule

• Loop of Henle

• Collecting Tubule

Renal Corpuscle (2 components)

Glomerular Capsule

• double walled cup formed by the proximal end of the renal tubule

• aka Bowman’s Capsule

Glomerulus

• tuft of capillary loops which protrudes into the Bowman’s capsule

• located in kidney’s cortex

Glomerular Filtration (+ why its important) + Glomerular Filtrate

a process occurring in the corpuscles

• important in urine production → some of the blood plasma (except for protein) passes out of the glomerular capillaries and exits the space (capsular space ) between the inner + outer layers of the capsule

Glomerular Filtrate = fluid formed by this process

Glomerular Capsule Layers (2) (+ what inner layer contains)

Outer (parietal) Layer = simple squamous epithelial

Inner (visceral) Layer = composed of specialized cells

• Podocytes = have several processes that branch to form 3 processes

Foot Processes of Podocytes (nickname + location + what they form)

aka Pedicels

• adheres to basal lamina (basement membrane) covering the capillary endothelium

• foot processes of one podocyte interlock with those of adjacent podocytes → forms small network of small clefts between them (filtration slits)

• Filtration Slits = slit pores; restricts passage of some molecules

Glomerular Capillaries (+ what they form)

endothelium formed by a single layer of squamous cells

• cells have small pores → filtration barrier

Filtration Barrier (what it does + 3 things it consists of)

separation between the blood in glomerular capillaries from the capsular space

Consists of

1. fenestrated epithelium

2. basal lamina (basement membrane of the capillary endothelium

3. the slit membranes that cover the Filtration Slits

What size/amount of substances are able to pass through the Filtration Barrier and what does that mean for Glomerular Filtrate?

many substances are able to pass through the barrier; these substances are less than 3nm diameter

• this means that the Glomerular Filtrate is comprised of most substances present in the plasma EXCEPT most plasma proteins

Charged Glycoproteins and their relationship with the Filtration Barrier (+ speed of charged glycoproteins)

Negatively charged Glycoproteins

• associated with the filtration barrier and influence the movement of molecules across the barrier

• b/c the barrier is negatively charged, negative proteins are repelled while positive ones can pass through

Order of speed/ability to pass through in Molecules

• + charged > neutral charged > negative charged

What can damage to the Filtration Membrane Cause? (2)

• Albuminuria (proteinuria)

• Hematuria (blood)

What makes up the Renal Tubule? (3)

• Proximal Convoluted Tubule

• Distal Convoluted Tubule

• Loop of Henle

Proximal Convoluted Tubule (def + shape/size + cell type/function)

region of the renal tubule beyond the glomerular capsule whose lumen is continuous with the capsular space

• located in cortex; twisted

• wall = single layer of columnar cells with microvilli → causes increased surface area for reabsorption + secretion

Ascending + Descending Limbs of LoH (+ cell type)

Descending limb

• descends into medulla

• wall = thin squamous epithelial → thin segment of loop

Ascending

• formed in medulla

• wall = cuboidal cells (in thick) and squamous cells (in thin)

Distal Convoluted Tubule (+ cell type)

highly coiled region beyond the distal straight tubule

• wall = single layer of cuboidal cells with few microvilli

Collecting Tubule (+ relationship with papillary ducts)

a large tubule in which DCT’s of several nephrons empty into

• passes through a medullary renal pyramid → joining together of adjacent collecting tubules to form larger ducts (papillary ducts) that open on the papilla → minor calyx

Renal Arteries (how much blood they deliver + kidney cell nutrition + purpose of blood flow)

Each kidney receives a renal artery = a major branch from the descending aorta

• kidneys receive 20% of the total CO (1.1 L/min of blood passing through the two kidneys)

• little of this blood is for kidney cell nutrition

• Purpose of large blood flow = maintenance of the blood homeostasis

Flow chart of blood through kidney starting at Renal Arteries

Renal arteries → Interlobar arteries → Arcuate arteries → Afferent arterioles →Glomerulus → Efferent arterioles → Peritubular capillaries OR Vasa Recta → Interlobular veins → Arcuate veins → Interlobar veins → Renal veins

Interlobar Arteries + Arcuate Arteries

Interlobar arteries - travel between the pyramids (lobes)

Arcuate arteries - arching branches at the bases of the pyramids; run parallel to the kidney surface

Interlobular Arteries - travel through the cortex toward the kidney surface

Afferent Arterioles + Efferent Arterioles

Afferent Arterioles - supply renal corpuscles to form the capillary network

• capillary network/bed = Glomerulus

• Glomerular Filtrate is formed here

Efferent Arterioles - blood leaves the glomerulus through this arteriole

• forms either Peritubular Capillaries or Vasa Recta (both are capillary beds)

Vasa Recta (location + where they supply + their role) vs Peritubular Capillaries (location)

Peritubular Capillaries - form networks surrounding the renal tubules

• located in cortical nephrons (renal cortex)

Vasa Recta - thin-walled vessels that supply the loop of Henle + collecting tubules in the medulla

• IMPORTANT role in urine concentration

• found in juxtamedullary nephrons (renal medulla)

What empties into the interlobular veins + what is formed after

Peritubular capillaries or Vasa Recta empty into Interlobular Veins

• Interlobular veins merge and eventually form renal veins (as seen in flow chart of blood)

Why is the presence of arterioles leading to/from the Glomerulus significant?

1. The smooth muscle in arteriole walls permits constriction or dilation depending on what is needed

2. This leads to fairly constant blood pressure in the Glomerulus

3. Thus there is efficient kidney function

Glomerular Capillaries vs Peritubular Capillaries (or Vasa Recta)

Glomerular Capillaries - produces filtrate

• involved in filtration

• fenestrated

• no gas exchange

Peritubular Capillaries/Vasa Recta - reabsorbs filtrate

• involved in secretion

Juxtaglomerular Complex + location (2)

a combination of specialized tubular + vascular cells located at the vascular pole where the afferent + efferent arterioles enter/leave the glomerulus

• located in cortex

• where the tubule (ascending limb of LOH or DCT) contacts the afferent arteriole

Two cell types in Juxtaglomerular Complex (+ what they are involved in and what one of them secretes)

Juxtaglomerular cells - specialized smooth muscle cells of the afferent arteriole that contain secretory granules (which then contains renin)

Macula Densa cells - region of the tubule which contacts the juxtaglomerular cells

• cells appear taller

Both cells are involved in blood pressure + Na+ regulation

Three Basic Renal Processes (+ active or passive for each process)

Glomerular Filtration - plasma filtered out of the Glomerular Capillaries into the Bowman/Glomerular Capsule

• NOT selective, but passive

• produces glomerular filtrate

Tubular Reabsorption - process which removed water, ions, glucose, etc from the tubular fluid and returns it to the blood as it flows through the Peritubular Caps/Vasa Recta

• can be active or passive

Tubular Secretion - materials that enter the tubular fluid which didn’t enter the glomerular capsule during filtration

• can be active or passive

• removed substances from blood

Glomerular Filtrate

the filtrate in the Renal Tubules

• water + other plasma that enter the capsule

What control is secretion + reabsorption under?

What can the fluid remaining in the tubules be excreted as?

Secretion + Reabsorption under Hormonal control

Fluid remaining in tubules can eventually be excreted as Urine