TTU ZOOL 2403 Final Exam Dr. Boros

What does the Kidney do?

Produces Urine

Functions of Kidney

1. Excretion

-removal of wastes from body fluids into urine

2. Regulation of Blood

-Ions

a. control blood Na+ (sodium), K+ (potassium),

and Cl- (chloride) levels

-ph

a. control blood H+ (hydrogen) and HCO3-

(bicarbonate) levels

-Pressure and Volume

a. control blood fluid volume and therefore

blood pressure

What three processes do the Kidneys use to perform their functions?

-Filtration of water, ions, nutrients, and waste products from the blood

-Reabsorption of most of the water, ions, and nutrients back into the blood

-Excretion of metabolic wastes into the urine

Describe the Drinking Process

Water is absorbed by the gastrointestinal (GI) tract into the blood, which goes to the Renal Arteries which supply the kidneys and then becomes urine.

We lose water constantly through our...

-Skin

-Lungs

-Digestive System

The kidneys can regulate what because of what?

They can regulate water volume because they can concentrate or dilute the urine

Among other things, what are the kidneys responsible for?

The kidneys are responsible for our ability to survive on land without dehydrating

Where are the kidneys located and what are they protected by?

The Kidneys are located on either side of the . vertebral column and are partly protected by the ribcage

What are the 2 divisions of the kidney?

The Renal Cortex and the Renal Medulla

Describe the Renal Cortex

The Renal Cortex is the outer portion of the kidney

Describe the Renal Medulla

1. inner portion of the kidney

2. separated into renal pyramids by renal columns

How is blood supplied to the kidneys?

1. Each Kidney receives blood from a Renal Artery

2. The Renal Artery Branches into many smaller and smaller arteries

3. These smaller arteries travel between renal pyramids within the Renal Columns

4. They ultimately deliver the blood via the arterioles to a capillary network called the "Glomerulus"

What is the percentage of total cardiac output that kidneys receive?

20-25%

How many liters of blood flow through the kidneys each minute?

1.2 Liters

How many times a day is the entire blood volume filtered by the kidneys?

60 times

How long would it take for the blood filtered by the kidneys to be excreted if it were excreted in its entirety?

25 minutes

What percentage of the filtered blood is returned to the cardiovascular system?

99%

Composition of the Kidneys

1. Nephrons

2. A Collecting System

How many nephrons does the kidney contain?

The kidney contains about 1.25 million nephrons which are 85 miles in combined length

What is the Nephron?

The Nephron is the functional unit of the Kidney

Composition of the Nephron

1. Renal Corpuscle

2. Renal Tubule

Where does Urine Production begin?

In the Nephron

What occurs in the Nephron?

1. Blood is filtered into the Nephron

2. Composition changes during the process

Composition of the Renal Corpuscle

1. Glomerulus

2. Bowman's Capsule

3. Urinary Space

What does the Glomerulus intertwine with?

The network of capillaries

Where does the glomerulus receive blood and where does blood leave the glomerulus?

The glomerulus receives blood from the afferent arteriole and blood leaves the glomerulus through the efferent arteriole

What is the Bowman's Capsule?

A sac-like structure that surrounds the glomerulus

What is the Bowman's capsule composed of?

Squamous Epithelial Cells

What does the Bowman's Capsule enclose?

the Urinary Space

Define Urinary Space

The space between the inner layer lining of the glomerulus and the outer layer of the Bowman's capsule

Where does Filtration of fluid from Blood into the Nephron occur?

In the Renal Corpuscle

Describe Filtration of fluid from Blood into the Nephron

Blood Pressure

1. forces water and dissolved solutes out of the

glomerulus and into the urinary space

2. produces a protein-free solution called filtrate

What are the 3 Layers of Filtration?

1. The glomerulus (capillary): endothelial cell layer

2. Middle connective tissue layer

3. Inner lining of the Bowman's capsule: epithelial cell layer

What is the Glomerular Endothelial Layer?

Pores in the endothelial cells lining the glomerular capillaries

Function of the Glomerular Endothelial Layer

They are small enough to prevent passages of the blood cells into the filtrate, but they do allow some proteins to get through

Composition of the Podocyte Layer of the Inner Lining of the Bowman's Capsule

It is made up of epithelial cells, "foot cells", called podocytes.

What are Podocytes composed of?

They're composed of many foot processes called pedicels

Describe the role of the Podocyte Layer of the Inner Lining of the Bowman's Capsule

There are filtration slits between adjacent pedicels of podocyte which are smaller than the pores of the endothelial cells.

They only allow water and dissolved solutes from the blood and into the urinary space.

What causes kidney disease and kidney failure?

The connective tissue layer between the pores and slits can become clogged with debris

What is the Renal Tubule?

A long, U-shaped tube extending from the cortex into the medulla and back into the cortex

Where does the Renal Tubule begin?

The Renal Corpuscle

Composition of Renal Tubule

1. Proximal Convoluted Tubule (PCT)

2. Loop of Henle

3. Distal Convoluted Tubule (DCT)

Where does the Renal Tubule end?

The collecting duct

Composition of the Wall of the Tubule

-The wall of the Renal Tubule is composed of epithelial cells

-They can be anything form squamous to columnar cells

What determines the type of epithelial cell that lines the Renal Tubule?

The degree of activity of that portion of the tubule

Functions of the Renal Tubule cells

1. Reabsorb nutrients and water form the filtrate

2. Return said nutrients and water to the blood

3. Excrete what's left in the tubule into the urine

What happens to the filtrate traveling along the tubule?

The composition of the filtrate changes

How do the reabsorbed water and solutes return to the blood?

-Peritubular Capillaries and Vasa Recta

Describe the Peritubular Capillaries and the Vasa Recta

-Both are branches of the efferent arteriole

-They drain blood into the venous system and back into the heart

Proximal Convoluted Tubule

The first segment of the renal tubule

What occurs in the Proximal Convoluted Tubule?

Bulk reabsorption of filtrate

What percentage of the filtrate is reabsorbed in the PCT?

60-70%

What do the epithelial cells have in the PCT and what purpose do they serve?

Epithelial cells have microvilli to increase surface area for absorption

Loop of Henle

The middle segment of the renal tubule

What is the Loop of Henle composed of and what occurs?

Composed of:

-a descending limb where fluid flows "down" into the medulla

-an ascending limb where fluid flows "back up" into the cortex

How does the Loop of Henle concentrate urine?

1. Na+ and Cl- are actively pumped out of the ascending limb and back into the bloodstream

2. Water follows out of the descending limb and back into the bloodstream

3. Tubular fluid becomes very concentrated

4. Urea (the most abundant organic waste from amino acid breakdown) is now the main solute left in the tubular fluid, hence urine

Distal Convoluted Tube

The last segment of the renal tubule

Describe the epithelial cells lining the DCT

1. They're smaller than those of the PCT and do not have microvilli

2. They're less active than the cell of the PCT

3. These cells are more highly specialized than the cells of the PCT

What occurs in the DCT and why?

-Further adjustments are to the filtrate are made

-Very selective reabsorption occurs here in response to hormones

What is the purpose of selective reabsorption in the DCT?

To regulate:

-blood pressure and volume

-blood ph

What type of structure is the Juxtaglomerular Apparatus?

Endocrine

Composition of Juxtaglomerular Apparatus

-Macula densa

-Juxtaglomerular (JG) cells

Macula Densa

specialized epithelial cells in the DCT

Juxtaglomerular (JG) cells

specialized smooth muscle cells of the afferent arteriole

What do the JG cells sense?

Decreased blood pressure

What happens when JG cells sense decreased blood pressure?

JG cells release renin (a hormone)

What does renin activate?

Renin activates angiotensin (another hormone)

What does angiotensin cause?

-Vasoconstriction

-Secretion of aldosterone by the adrenal cortex

What does aldosterone cause?

It causes DCT cells to increase Na+ reabsorption (water always follows Na+)

What happens to the Na+ and water? What does it result in?

Both are returned to the blood, which results in increased blood pressure and increased volume

What do stretch receptors of the heart walls sense?

Increased blood pressure or volume

What happens when the stretch receptors of the heart wall sense increased blood pressure?

The atria of the heart releases Atrial Natriuretic Peptide (ANP)

What does the release of ANP cause?

Decrease in Na+ and water reabsorption at the DCT so there is increased Na+ and water excretion into the urine

What does the release of ANP result in?

Decreased blood pressure and volume

What does decreased blood pressure lead to?

-The release of Renin which releases Angiotensin which releases Aldosterone which leads to:

1. increased Na+ and water reabsorption at DCT

2. increased blood volume and therefore

pressure

-Less water in the urine

-Urine becomes more concentrated

What does increased blood pressure lead to?

-The release of Atrial Natriuretic Peptide (ANP)

which leads to

1. decreased Na+ and water reabsorption at DCT

2. decreased blood volume and therefore

pressure

-More water in the urine

-Urine becomes dilute

How does the DCT regulate blood pH?

-H+ excretion into the forming urine

- HCO3- (bicarbonate) production and

reabsorption into the blood

What is the function of HCO3?

HCO3 buffers the blood

What does the Collecting Duct determine?

The final composition and volume of urine

Hypothalamic neurons are stimulated by either...

1. decreased blood pressure or...

2. increased blood Na+/Cl- concentration

Which hormone do the Hypothalamic neurons release and what does that hormone cause?

Hypothalamic neurons release Antidiuretic Hormone (ADH) and causes increased water reabsorption at the Collecting Duct

What do collecting ducts form when they converge?

Collecting ducts converge to empty into a minor calyx

Where does the minor calyx end?

The minor calyx ends at the renal papilla of each renal pyramid

Minor Calyx

-cup like structure surrounding each renal pyramid

-collects urine from each renal pyramid

-several join to form a major calyx

Major Calyx

-collects urine from several minor calyces

-join to form the Renal Pelvis

Renal Pelvis

-acts as a funnel to drain urine from the kidney to the ureter

What type of muscle makes up the Ureters?

Smooth muscle

Function of the Ureter

-transports urine towards the urinary bladder

-collects urine from the renal pelvis

-empties urine into the urinary bladder

-prevents the back-flow of urine

How do the Ureters prevent the back-flow of urine?

THey flatten as the bladder fills with urine and when the bladder contracts to void the urine

Urinary Bladder

-hollow, muscular organ (smooth muscle)

-temporary reservoir for urine storage

How much urine can the urinary bladder hold to be full?

1 liter

Urothelium

-lines the urinary bladder

-also known as transitional epithelium

Composition of the Urothelium

Composed of cells that:

1. are impermeable to water

2. can rearrange themselves and spread out as the

bladder fills with urine

How long is the male urethra?

7-8 inches long

Where does the male urethra begin?

Begins at the inferior pole of the bladder

What does the male urethra pass through?

The prostate gland and the penis

How long is the female urethra?

1-2 inches long

What does the shortness of the female urethra leave a female more prone to?

Females are more prone to frequent infection of the urinary bladder

External Urethral Sphincter

Skeletal muscle that surrounds the urethra in both sexes

Describe the function of the External Urethral Sphincter

It's a voluntary muscle, so it's under conscious control.

-Relaxation permits micturition (urination)