Chapter 11 - Homeostasis

Question 1

Homeostasis (definition and examples)

Answer 1

(

In living organisms this includes:

• The balance between acidity and alkalinity (pH)
• temperature maintenance (Thermoregulation)
• Osmotic/oncotic pressure (Osmoregulation)
• Blood glucose levels
• Blood O₂/CO₂ balance

Question 2

Osmoregulation

Answer 2

Maintenance of water and solute concentrations

Question 3

Thermoregulation

Answer 3

Maintenance of a constant internal body temperature

Question 4

Why is homeostasis critical?

Answer 4

Homeostasis allows for the maintenance of an internal environment in the face of a changing external environment. This is critical for maintaing regular functioning of life processes

Question 5

Kidney: functions

Answer 5

1. Excrete waste products (i.e., urea, uric acid, ammonia, phosphate)
2. Maintain homeostasis: fluid volume; solute composition (Osmoregulation)
3. Control plasma pH

Question 6

Kidney: diagram

Answer 6

Question 7

Kidney Cortex (compnents)

Answer 7

Outermost layer of the kidney. Consists of renal corpuscle (glomerulus & Bowman’s capsule), Proximal tubule, and Distal Tubule. Collecting duct straddles cortex/medulla.

Question 8

Medulla

Answer 8

Innermost layer of the kidney, sits beneath the cortex. Consists of descending / ascending limbs of the loop of Henle, and the vasa recta (not formally part of the nephron). The collecting duct straddles cortex/medulla.

Question 9

Flow of blood through kidney

Answer 9

Arteries (Somatic) → Afferent arteriole → Glomerulus → Efferent Arteriole → Vasa Recta (if medullary nephron) → Arteries (Somatic)

Question 10

Nephron

(and components, in order)

Answer 10

Functional unit of kidney:
Renal corpuscle → proximal tubule → loop of Henle → distal tubule → collecting duct

Question 11

Renal corpuscle

Answer 11

Region of nephron (kidney) where filtration occurs. Made up of glomerulus and Bowman’s capsule. Located in cortex.

Question 12

Filtrate

Answer 12

The material that passes from the blood vesels into Bowman’s capsule

Question 13

Proximal tubule

Answer 13

Region of nephron (kidney) where reabsorption (water, glucose, proteins, etc.) and secretion (drugs, toxins, etc.) occurs. Located in cortex.

Question 14

Distal tubule

Answer 14

Region of nephron (kidney) where osmolarity is lowered. In presence of ADH, water flows out of tubule, concentrating filtrate. Located in cortex.

Question 15

Collecting duct

Answer 15

Region of nephron (kidney) that carries filtrate into highly osmotic medulla. In presence of ADH, concentrates urine. (Normally impremeable to water, but becomes permeable w/ADH.) Straddles cortex/medulla.

Question 16

Juxaglomerular apparatus

Answer 16

Monitors filtrate pressure in the distal tubule.

Question 17

Vasa recta

Answer 17

A series of capillaries in the medulla parallel to the loop of Henle. These vessels branch off the efferent arterioles of nephrons closest to the medulla, enter the medulla, and surround the loop of Henle. They aid in maintaining the concentration gradient and are partially responsible for the kidney’s ability to produce concentrated urine.

Question 18

Loop of Henle

Answer 18

Region of nephron (kidney) where solutes are concentrated. Loop of Henle is located in the medulla. Descending loop: only permeable to water. Ascending loop: impermeable to water; actively transports Na⁺ and Cl^-into kidney.

Question 19

How does plasma enter the glomerulus of the kidney for filtration?

Answer 19

Hydrostatic pressure forces plasma through sieve-like “fenestrations” (which keep out blood cells and large proteins).

Question 20

What are the three fundamental mechanisms used by the kidney to maintain homeostasis and osmoregulation.

(These determine urinary excretion rate)

Answer 20

Urinary excretion rate (UER) is determined by:

• Filtration
• Secretion
• Reabsorption

UER = F – R + S

Question 21

Filtration (definition and locations in kidney)

Answer 21

Selective permeability of molecules based on size and charge. First step of kidney functiuon. Occurs at the glomerulus. The filtrate is isotonic to the blood so that neither Bowman’s Capsule nor the capillaries will swell.

Question 22

Secretion (definition and locations in kidney)

Answer 22

Transfer of materials from the circulatory system to the renal tubules for excretion. Excess molecules, such as salts, acids/bases, urea, waste products, and toxins are secreted from the peritubular capillaries directly into the distal tubule, bypassing the glomerulus. This occurs by both active and passive transport.

Question 23

Reabsorption (definition and locations in kidney)

Answer 23

The process by which solutes and water are removed from the tubular fluid and transported back into the circulation. Glucose, amino acids, vitamins, Na⁺, Cl^- and H₂O are all reabsorbed by the tubules of the nephron. Note, anything that makes it into the filtrate but is not reabsorbed will be lost from the body.

Question 24

Kidney filtration and reabsorption sites (diagram)

Answer 24

Question 25

What two physical principles of solute movement work in concert in the nephron to allow for selective reabsorption and excretion? What is this called?

Answer 25

* **Selective permeability** – While small molecules are non-selectively filtered through the glomerulus, specific molecules are able to pass from the filtrate into the tubules, while waste material remains, eventually to be excreted. * **Osmolarity gradient** – Alteration of the osmolarity of the interstitium generates a gradient that, coupled with selective permeability, allows for selective reabsorption. While the cortex is isotonic, the osmolarity becomes increasingly hypertonic with descent into the medulla. The combination of these principles work as a **countercurrent multiplyer system**.

Question 26

Filtration, Secretion, and Reabsortpion in the Nephron (diagram)

Answer 26

Question 27

Filtrate flow (list)

Answer 27

**Re:** reabsorbed into interstitium, **Sec:** secreted into filtrate * Proximal tubule: * **Re:** Na⁺, Amino acids, glucose, vitamins, Cl^-, H₂O * **Sec**: H⁺, K⁺, NH₃, Urea * Descending limb: * **Re: **H₂O * **Sec:****​ **Urea * Ascending limb: * **​Re: **Na⁺, Cl^- * **Sec: **Urea * **​**Distal Tubule: * **​Re: **Na⁺, Cl^-, H₂O * **Sec: **H⁺, K⁺, NH₃ * **​**Collecting Duct: * **Re:** H₂O * **Sec: **None

Question 28

How is water moved into and out of the kidney?

Answer 28

Water is not reabsorbed alone, and is usually not pumped at all. The kidney moves ions (primarily Na⁺ and Cl^-) to create gradients taht water will follow by osmosis.

Question 29

What does the final concentration of urine depend on?

Answer 29

The permeability of the collecting duct. As permeability increases, so does water removal,which concentrates urine. Ultimately the duct itself works under the directions of antidiuretic hormone (ADH) and aldosterone.

Question 30

Renin

Answer 30

Enzyme secreted by granular cells of juxtaglomerular apparatus. activates angiotensin, which stimulates the adrenal cortex to secrete aldosterone.

Question 31

Aldosterone: effect on kidney?

Answer 31

Aldosterone acts on distal tubule and is regulates water uptake by stimulating formation of membrane proteins that reabsorb Na⁺ and excrete K⁺. Na⁺ reabsorption generates an osmotic gradient that leads to H₂O uptake by osmosis. Aldosterone raises blood pressure by increasing blood volume.

Question 32

Aldosterone: regulation

Answer 32

A steroid hormone produced in the adrenal cortex and secreted in response to decreased blood volume (i.e. decreased blood pressure, aka hypotension). Aldosterone is released from the adrenal glands in response to an increase in angiotensin, which itself is positively regulated by renin.

Question 33

ADH: effect on kidney?

Answer 33

Antidiuretic hormone; aka vasopressin. Increases water retention. Acts at the collecting duct to directly increase permeability of cells to water, allowing water to flow OUT of tubule and concentrating urine. ADH is produced by the hypothalamus and stored in the posterior pituitary.

Question 34

ADH: generation and regulation

Answer 34

ADH is a peptide hormone that directly alters the permeability of the collecting duct. It is made in the hypothalamus, stored in the posterior pituitary, and secreted when blood osmolarity is high. Alcohol and caffein both inhibit ADH, leading to frequent excretion of dilute urine.

Question 35

Compare the mechanisms of action of aldosterone and ADH in regulating osmolarity.

Answer 35

* Aldosterone increases sodium reabsorption in the collecting, which generates an osmotic gradient that water follows. * ADH alters the permeability of the collecting duct, making it more leaky to water such that it will more easily enter the interstium.

Question 36

What three compunds should always be absent from healthy urine?

Answer 36

The presence of any of these molecules in urine indicates kidney pathology: 1. Blood - too large to filter (glomerular pathology) 2. Protein - too large to filter (glomerular pathology) 3. Glucose - typically reabsorbed (tubular pathology)

Question 37

What are the two most important liver functions in maintaining homeostasis?

Answer 37

* Blood glucose regulation * elimination of nitrogenous waste through urea

Question 38

Gluconeogenesis

Answer 38

A process in the liver by which glucose is produced using by-products from glycolysis, lipids, or fats.

Question 39

Glycogen

Answer 39

a polymerized form of glucose that is synthesized from circulating glucose molecules and stored in the liver during times of plenty. Glycogen is catabolized into glucose-6-phosphate, a glycolytic intermediate, and released into the bloodstream during times of famine.

Question 40

How do nitrogenous waste products arise, and how are they dealt with?

Answer 40

When there is a shortge of glucose, amino acids are used for vital processes such as celular respiration. In order to be useful in these processes, they must first undergo deamination, which would normally form the toxic ammonia as a byproduct. To prevent ammonia buildup the liver combines it with CO₂ to create urea, a non-toxic molecule excreted by the kidneys.

Question 41

Liver functions (Lots!)

Answer 41

* Detoxification * Vitamin storage * Erythrocyte destruction * Bile synthesis * Blood protein synthesis * Defense against antigens * Beta-oxidation of fatty acids to ketones * Interconversion of fats, carbohydrates, and amino acids

Question 42

## Footnote Large intestine: main functions

Answer 42

1. Water absorption 2. Electrolyte absorption ## Footnote

Question 43

E. coli in the large intestine: function ## Footnote

Answer 43

Symbiotic relationship. Bacteria get our "leftovers." They produce certain vitamins for us (K, B₁₂, thamin, riboflavin).

Question 44

## Footnote Skin: functions

Answer 44

1. Thermoregulation (reduce temp through sweat, but mostly radiation; increase temp by shunting blood away from skin capillaries or erecting hair to trap warm air) 2. Protection (physical barrier) 3. Environmental sensory input (temp, pressure, pain, touch) 4. Excretion (water, salt - this is independent of sweating) 5. Immunity (specialized epidermal cells part of immune system) 6. Blood reservoir (dermis) 7. Vitamin D synthesis

Question 45

Skin: components ## Footnote

Answer 45

1. Epidermis 2. Dermis 3. Subcutaneous tissue

Question 46

Epidermis: composition, cell types ## Footnote

Answer 46

Upper layer of skin, epithelial, avascular (no blood vessels). Five strata (layers). Stem cells at bottom divide continually to produce the following four cell types: 1. **Keratinocytes** (top layer; produce kertain to waterproof skin) 2. **Melanocytes** (transfer melanin pigment to keratinocytes) 3. **Langerhans cells** (interact w/helper T-cells) 4. **Merkel cells** (deepest layer; attach to sensory neurons; help w/touch)

Question 47

Dermis

Answer 47

Connective tissue of skin. Below epidermis. Subdivided into the papillary and reticular layer. Contains blood vessels, sense organs (nerves), sweat glands, abd the bulbs of hair follicles. Collagen and elastic fibers allow for strength/elasticity. Derived from the mesoderm.

Question 48

Hypodermis

Answer 48

Subcutaneous skin tissue (under dermis). The fat of this layer helps insulate body. Serves to bind the dermis to the body.

Question 49

Integumentary system

Answer 49

Skin, hair, nails, glands, some nerve endings form this system.

Question 50

Skin: Diagram

Answer 50

Question 51

Epidermis: sublayers and function

Answer 51

Serves as a protective barrier against microbial attack. Derived from the ectoderm. 1. Stratum basalis 2. stratum spinosum 3. stratum granulosum 4. stratum lucidum 5. stratum corneum