Chapter 25 & 26 - The Urinary System and Excretion and Fluid Balance

Question 1

Materials Excreted by the Urinary System

Answer 1

Carbon dioxide
water
Any substance which is in excess in the body
Nitrogenous wastes, such as urea, creatinine, and uric acid.

Question 2

Excretion and Homeostasis

Answer 2

Because even essential substances can be excreted if in too a quantity, excretion plays a major role in maintaining the proper concentrations for the body fluids. Consequently is a major contributor to homeostasis

Question 3

Urinary System Anatomy

Answer 3

• The kidneys
• The ureters
• The urinary bladder
• The urethra

Question 4

Kidney Functions

Answer 4

• Regulate the composition and volume of blood and body fluids
• Excrete waste from the blood
• Regulate erythropoiesis
• Aid in regulating pH
• Regulate blood pressure by releasing Renin which activates the angiotensin system
• Assists the liver in detoxification, deamination, and gluconeogenesis

Question 5

External Anatomy of the Kidney

Answer 5

The kidneys resemble large beans which an indent called the hilus, which is where the ureter exits. There are 3 tissue layers which surround the kidney.

Question 6

Renal Capsule

Answer 6

The innermost layer. A fibrous membrane that protects against trauma.

Question 7

Adipose Capsule

Answer 7

The middle layer. Protects against shock and helps hold the kidneys in place. A mass of fatty tissue, a cushiony layer.

Question 8

Renal Fascia

Answer 8

A very thin connective tissue. It anchors the kidney to the body wall. It’s very very thin and may become disconnected. It also surrounds the adrenal glands

Question 9

Renal Medulla

Answer 9

Innermost layer. It consists of 5 to 14 renal pyramids. The loop of Henle is usually found here. The pyramids face outwards, and their apex, the renal papillae, are directed towards the center.

Question 10

Renal Cortex

Answer 10

The outer layer. It dips down in between the pyramids forming the renal columns, where most of the nephrons are found.

Question 11

Minor Calyx, Major Calyx, and Renal Pelvis

Answer 11

Each pyramid empties into a funnel shaped space, the minor calyx, which then becomes larger and forms the major calyces. They then form a larger space, the renal pelvis, which empties into the ureter.

Question 12

Nephron

Answer 12

The sire of urine formation and consequently represents the functional unit of the kidney.

Question 13

Glomerular Capsule

Answer 13

A filter, the beginning of the kidney tube. Double walled and has specialized capillaries which form a ball called the glomerulus. The capillaries are fenestrated, making them very permeable. The outer layer is composed of squamous epithelium, the inner layer has special epithelial cells called podocytes, which have slits.

Question 14

Proximal Convoluted Tubule

Answer 14

Highly twisted, lined with cells that have microvilli and mitochondria.

Question 15

Loop of Henle

Answer 15

Where the tube straightens out, it forms a long hairpin shape. Two parts, the descending which is thinner, and the ascending which is thicker.

Question 16

Distal Convoluted Tubule

Answer 16

The last of the renal tubule. It is highly twisted and surrounded by capillaries.

Question 17

Collecting Ducts

Answer 17

The distal convoluted tubule empties out here. May have many nephrons emptying out here. Not technically part of the nephron.

Question 18

Types of Nephrons

Answer 18

(1) Cortical Nephrons = Glomeruli are found on the outer portion of the cortex. Lack a loop of Henle and usually don’t even reach down into the medulla. About 85% of nephrons.
(2) Juxtamedullary Nephron - The glomerulus lies in the cortex close to the border of the medulla. It has a loop of Henle which penetrates deep into the medulla. Their major role is water balance.

Question 19

Circulation in the Kidney

Answer 19

Renal artery —> segmental arteries —> lobar arteries —> interlobar arteries —> arcuate arteries —> interlobular arteries —> afferent arterioles —> glomerulus —> efferent arterioles —> peritubular capillary beds.

Question 20

Renal Plexus

Answer 20

The nerve supply of the kidney

Question 21

Nephron Function

Answer 21

Urine formation. Filtration occurs across glomerular walls; nutrient absorption occurs primarily in the proximal convoluted tubule; secretion occurs primarily in the distal convoluted tubule; the loop of Henle regulates water and Na+ loss.

Question 22

Filtration

Answer 22

Essentially the same process that occurs across every capillary wall, but much more efficient in the glomerulus.

Question 23

Glomerular Capillary Membrane

Answer 23

Much more permeable than the average capillary. It has completely open pores and only a basement membrane. It has a very high surface area.

Question 24

Glomerular Blood Pressure

Answer 24

Very high, about 60 mmHg. Because of this, the efferent arteriole is smaller in diameter than the afferent. The osmotic pressure is an opposing force which tries to pull the fluid back into the glomerulus, about 30 mmHg. Pressure between the layers is about 20 mmHg. Net is about 10 mmHg.

Question 25

Glomerular Filtration Rate (GFR)

Answer 25

About 25% of the cardiac output flows through the kidney. Insulin is the standard at 125. If theres a clearance value lower than that, it means the substance is partially reabsorbed. If it’s higher, it means the tubule cells must be secreting.

Question 26

Reabsorption

Answer 26

It’s highly selective compared to filtration. Most solutes are reabsorbed by active transport, some co-transport, and some diffusion. Nutrients like glucose and AA are too important to be lost, so the goal is for 100% to be reabsorbed. which doesn’t always happen.

Question 27

Threshold Value

Answer 27

The concentration in the plasma that must be exceeded before it appears in the urine. The tubular maximum which equates to the maximum amount of the substrate that the tubule can reabsorb, the rest is lost in urine.

Question 28

Secretion

Answer 28

Substances are actively secreted from the blood to the nephron tubule. Only a few can be secreted, H+, K, NH3, creatinine, and some drugs. This helps regulate pH.

Question 29

Micturition

Answer 29

This is the elimination of urine from the bladder.

Question 30

Water and Electrolyte Balance

Answer 30

Water is the single largest constituent of the body and accounts for 45 to 75% of the body weight. It is essential for the maintenance of homeostasis.

Question 31

Fluid Compartments

Answer 31

There are two major compartments, the intracellular fluid, and the extracellular fluid. The extracellular can be further divided into the tissue fluid and the plasma . There must be a dynamic balance between these compartments. Osmotic shifts between the compartments cause the kidney to directly regulate water.

Question 32

Sodium and Water Reabsorption

Answer 32

Na+ is the most abundant cation in the body. It is largely responsible for the bulk of water reabsorption. The bulk of Na+ is reabsorbed in the PCT, therefore most water is reabsorbed there too.

Question 33

Aldosterone

Answer 33

A steroid hormone produced by the adrenal cortex. It causes the kidney tubules to increase sodium transport and thus increases sodium reabsorption. Sodium retention always results in water retention.

Question 34

Atrial Natriuretic Factor

Answer 34

Hormone released by the atrial myocardial cells. It inhibits the release of renin by the kidney and therefore modifies the activity of the angiotensin system. This results in reduced aldosterone, reduced sodium, reduced water retention, and reduced blood pressure.

Question 35

Juxtamedullary Cells Decrease the Blood Supply to the Kidney

Answer 35

Renin is produced. Then angiotensin is produced it activates angiotensin I, which then activates angiotensin II. This constricts the arterioles and increases blood pressure. The SNS is stimulated by the constricted arterioles, it causes them to constrict even more and thus stimulates Renin production.

Question 36

The Kidney Produces 3 Main Hormones

Answer 36

(1) Renin
(2) EPO
(3) Calcitrol

Question 37

Water Reabsorption

Answer 37

If the body has an excess of water, the kidney will produce a copious amount of dilute urine. If the body is dehydrated, the kidney will produce a low volume of concentrated urine which is dark in color. 80% of water reabsorption occurs in the PCT.

Question 38

Mechanism of the Loop of Henle

Answer 38

As the urine moves down the descending it becomes more concentrated as it moves up the ascending it loses some of that concentration. Here Cl- leaves and Na+ follows, but water stays.

Question 39

Role of the Vasa Recta

Answer 39

This loop in the peritubular capillary bed parallels the loop of Henle. Blood flow here is in the opposite direction of urine flow in the loop. It functions to maintain the medullary concentration gradient developed by the loop of Henle.

Question 40

Absorption in the Collecting Ducts

Answer 40

Water is reabsorbed back into the interstitial fluid and returned to the blood. Urea is concentrated, the tube is impermeable to it, so one can re enter. Na+ can be actively transported out of the collecting duct. It goes into the interstitial fluid.

Question 41

ADH

Answer 41

The amount of water reabsorbed from the collecting duct is controlled by ADH. It controls the final volume and concentration of urine. ADH is released by the neurohypophysis.

Question 42

Electrolytes

Answer 42

• Cl-: A negative ion regulated by aldosterone. It usually follows Na+. Together they’re responsible for fluid balance.
• K+: The most abundant cation in the intracellular fluid. Aldosterone has the opposite effect on K+ than on Na+. It promotes the secretion of K+, mostly in the DCT.
• Ca2+ & PO4 3-: Ions regulated by the endocrine hormones mainly he parathyroid.
• Mg 2+: Positive ion found in the skeleton, the heart, skeletal muscles, and liver. An increase in aldosterone will promote an increase in Mg secretion.

Question 43

Acid-Base Balance

Answer 43

The normal pH of arterial blood is 7.4, venous blood and interstitial fluid is 7.35, intracellular fluid is 7.0.

Question 44

Alkalosis

Answer 44

The pH of arterial blood is above 7.45

Question 45

Acidosis

Answer 45

The pH of arterial blood is below 7.35

Question 46

Bicarbonate Buffer System

Answer 46

The most common. It can pick up an H+ and become a weak acid or lose an H+ and become a weak base. It’s important in both intracellular and extracellular fluid pHs

Question 47

Phosphate Buffer System

Answer 47

The same as the bicarbonate system. It can pick up 3 H+s when the solution is too acidic, or lose 3 H+s if the solution is too basic.

Question 48

Protein Buffer System

Answer 48

It can give off the H+ from the carbonic acid, or it can pick up an extra H+ on the amine group.

Question 49

Respiratory Acidosis

Answer 49

Due to CO2 retention

Question 50

Respiratory Alkalosis

Answer 50

Hyperventilation leads to elevated blood pH.

Question 51

Metabolic Acidosis

Answer 51

Decrease in pH, usually caused by bicarbonate levels decreasing below homeostatic range.

Question 52

Metabolic Alkalosis

Answer 52

Increase in pH, caused by bicarbonate levels which are above homeostatic range.

Question 53

Diabetes Insipidus

Answer 53

The condition whereby either ADH is absent or in low concentration. Little or no water is reabsorbed and individuals with extreme deficiency may excrete 24 liters of urine per 24 hr period. It can be controlled by giving ADH inhalant.

Question 54

Glomerulonephritis

Answer 54

An inflammation of glomeruli. It is frequently caused by the deposition of antigen-antibody complexes in the glomeruli. Usually the antigen source is a streptococcal infection somewhere else in the body. The inflammatory response leads to blockage of many nephrons and increased permeability of the glomerulus. In severe cases total renal failure may occur.

Question 55

Kidney Stones

Answer 55

Crystals which form from several different substances in the renal pelvis. They may pass down the ureter to the bladder causing great pain and in some cases may block urine flow.

Question 56

Cystitis

Answer 56

Inflammation of the bladder, usually due to an infection, although chemical and physical factors can also cause it. Urination is frequent and painful. Blood may also appear in the urine.

Question 57

Diuretics

Answer 57

Substances that increase the volume of urine. They usually work by either blocking the release of ADH or by blocking it’s effect on the collecting duct. Alcohol depresses the nervous system and blocks the release of ADH which is manufactured by nerve cells.

Question 58

Dialysis

Answer 58

The blood is passed through a tube which permits the movement of urea and other small molecules out but blocks the passage of proteins and blood cells. The tube runs through a bath which contain the proper concentrations of vital plasma constituents such as glucose and vitamins. These prevent the diffusion outward of valuable plasma components.

Question 59

Effects of Aging

Answer 59

With age there is a progressive decrease in the GFR. Renal blood flow decreases from 10 mL per minute at ages 20-45 to roughly 5 mL per minute at ages 80-89. There is also a decrease in the ability to the tubules to concentrate urine and the results are increased volumes of urine with increased frequency of micturition.