Chapter 10: Homeostasis, Excretory And Skin

Question 1

What are the excretory system functions?

Answer 1

The excretory system functions are blood pressure, blood osmolarity, acid based balance, and removal of waste.

Question 2

What is the functional unit of the kidney?

Answer 2

The functional unit of the kidney is the nephron.

Question 3

What is the sequence of passage of blood through the vessels of the kidney?

Answer 3

The sequence of passage of blood through the kidney is renal artery, afferent arterioles, glomerulus, efferent arterioles, vasa recta, renal vein.

Question 4

Excretory system image

Answer 4

Question 5

Gross anatomy of the kidney image

Answer 5

Question 6

What is the bowman capsule?

Answer 6

The Bowman capsule filters blood coming from the afferent arterioles.

Question 7

Explain the kidney structure, including cortex, medulla, hilum, renal pelvis, vasa recta, renal artery, renal vein, ureter.

Answer 7

Each kidney is divided into cortex (outer layer) and medulla (inner layer). The renal pelvis is the widest part of the ureter where filtrate is excreted to the ureter. The renal artery brings oxygenated blood to the kidneys, the vasa recta brings blood to the second capillary system of the renal portal system around the loop of Henle, and the renal vein brings deoxygenated blood from the kidneys. The renal hilum is a deep slit in the center of the kidneys medial surface where the renal artery, renal vein, and ureter pass through.

Question 8

What is the renal portal system?

Answer 8

The renal portal system is a series of capillary beds in the kidneys. The first capillary bed is the glomerulus, the second capillary bed is the vasa recta surrounding and running countercurrent to the loop of Henle.

Question 9

Renal vasculature system and nephron, describing the anatomy and basic physiology.

Answer 9

Question 10

What is the detrusor muscle and what part of the nervous system causes the detrusor muscle to contract?

Answer 10

The detrusor muscle is the muscle lining the bladder and the parasympathetic nervous (remember that postsynaptic parasympathetic uses acetylcholine or are cholinergenic) system causes the detrusor muscle to contract (involuntary, autonomic)

Question 11

What are the two sphincters of the urethra?

Answer 11

The internal urethral sphincter, and the external urethral sphincter.

The internal urethral sphincter is made of smooth muscle and is under involuntary control, the external urethral sphincter consist of skeletal muscle and is under voluntary control.

Question 12

What is the micturition reflex?

Answer 12

The micturition reflex happens when the bladder is full and stretch receptors convey for the nervous system that the bladder requires emptying. Parasympathetic neurons fire and the detrusor muscle contracts and the internal urethral sphincter relaxes. The external sphincter is under somatic control and the individual must decide to utinate.

Question 13

What are the three different processes of the kidney regarding osmoregulation and blood volume regulation of the body?

Answer 13

Filtration, secretion, and reabsorption

Question 14

What is filtration regarding the kidneys, where does it occur, and how does it happen (hint if needed: starling forces)

Answer 14

Filtration is the process of mechanically filtering small compounds further into the nephron, filtration happens in the bowman capsule and is fed by afferent afferent arterioles. The filtrate (collected fluid) will not contain cells or proteins that are larger than the glomerular pores.

Filtration occurs due to a differentiation in hydrostatic pressure of the capillary and the bowman capsule. The osmotic pressure of the capillary in the bowman capsule are relatively equal (ISOTONIC) meaning that neither the capillary nor the capsule swell. This causes a net pressure in to the nephron.

Extra: starling forces are the net difference or balance of hydrostatic and osmotic pressures.

Question 15

What is secretion regarding the kidney, where does it happen?

Answer 15

Secretion is the movement of solutes from blood to filtrate anywhere beside the bowman capsule. Secretion can happen via passive diffusion or active transport/secretion. The nephrons are able to SECRETE salts, acids, bases, and urea directly into the tubule by active or passive transport.

Secretion and reabsorption are opposite. Secretion is blood to filtrate. Reabsorption is filtrate to blood or interstitium.

Question 16

What is reabsorption regarding the kidney, and where does it happen, where does it NOT happen through passive diffusion, what two hormones alter the quantity of water reabsorption?

Answer 16

Reabsorption refers to the movement of glucose, AA, vitamins, salts, WATER, acids, bases, and urea from the filtrate into the blood or interstitium. Most reabsorption happens in the proximal convoluted tubule, reabsorption happens in the descending and ascending loop of Henle, the distal convoluted tubule, and the collecting duct.

Aldosterone and ADH are hormones that alter the quantity of water reabsorbed in the kidneys.

Reabsorption of salts happens via active transport in the ascending loop of Henle.

Interesting, the ascending loop of Henle is only permeable to salts and not permeable to water (lacks aquaporins). The thicker membrane of the ascending loop of Henle is due to the presence of mitochondria to provide energy for active transport of salts (Na- and Cl-) against the osmotic gradient.

Question 17

Describe the RAAS pathway.

Answer 17

The RAAS pathway is the renin-angiotensin-aldosterone-system.

Decrease blood pressure to the afferent arterioles detected by baroreceptors cells in the juxtaglomerular cells causes release of renin from the kidney. Renin cleaves angiotensinogen (produced by the liver) into angiotensin I. Angiotensin I is metabolized by angiotensin-converting enzyme (in the lungs) to angiotensin II. Angiotensin II promotes the release of aldosterone by the adrenal cortex. Aldosterone alters the ability of the distal convoluted tubule and collecting duct to reabsorption sodium, thus causing reabsorption of water. Aldosterone also promotes excretion of potassium and hydrogen ions. Aldosterone does not change blood osmolarity.

Question 18

What does aldosterone do in the body, does aldosterone change blood osmolarity, what is the system that triggers aldosterone production (briefly), where is aldosterone made?

Answer 18

Aldosterone is a steroid hormone released by the kidney in response to the renin-angiotensin-aldosterone system (RAAS). Aldosterone alters the ability of the distal convoluted tubule and collecting duct to reabsorb sodium along with encouraging excretion of potassium and hydrogen ions as sort of an exchange. This causes water reabsorption and since water follows the sodium, aldosterone does not change blood osmolarity (because the exchange of fluid is isotonic) but does increase blood volume and thus pressure. Aldosterone is made and secreted by the adrenal cortex.

Question 19

What is an ACE inhibitor?

Answer 19

ACE inhibitors are angiotensin-converting-enzyme inhibitors. They work by exploiting the RAAS system by inhibiting the conversion of angiotensin I to angiotensin II. This will result in lowered blood pressure. This will reduce reabsorption of sodium while decreasing excretion of potassium and hydrogen ions.

Question 20

What is ADH, what does it do in the kidneys, does ADH increase blood osmolarity?

Answer 20

ADH is a peptide hormone synthesized in the hypothalamus and released by the posterior pituitary is response to high blood osmolarity. The hypothalamus detects high blood osmolarity using osmoreceptors that shrink when exposed to high blood osmolarity. Since ADH is a response to high blood osmolarity, ADH reduces blood osmolarity by altering the permeability of the collecting duct allowing more water reabsorption. Remembering the mechanism of release of ADH will help remember that ADH decreases blood osmolarity and thus blood pressure.

Question 21

Put simply, what are the two main goals of the kidneys?

Answer 21

The two main goals of the kidneys are:

to keep what the body needs and lose what it doesn’t

concentrate urine to preserve water.

Question 22

Reabsorption and secretion in the nephron (image), how do you interpret the image?

Answer 22

The segments that are horizontal in the diagram are primarily focused on the identity of particles in the urine, the segments that are vertical are primarily focused on the volume and concentration of urine (conservation of water). The lower portion of the graph demonstrates increased concentration in the interstitial fluid.

Question 23

Piece wise pathway of the nephron

Answer 23

Bowman capsule - proximal convoluted tubule - descending loop of Henle - ascending loop of Henle- distal convoluted tubule - collecting duct.

Question 24

What is the proximal convoluted tubule (PCT), what does it secrete and reabsorb, is there anything that makes it special, is the filtrate hypo iso or hypotonic?

Answer 24

The proximal convoluted tubule is the first region of the nephron that secretes and reabsorbs. The PCT filtrate is isotonic to the innerstitium.

The proximal convoluted tubule (PCT) is the region of the nephron located in the adrenal cortex that AA, glucose, water soluble vitamins, and majority of salts are reabsorbed (approximately 70% of filtered sodium will be reabsorbed to the interstitium from the PCT). The PCT also secretes (blood to filtrate) waste products such as hydrogen and potassium ions, ammonia, and urea.

It is special because it handles most of the filtered sodium reabsorption.

Question 25

What is the descending loop of Henle, where is is located, what is it ONLY permeable to (hint), describe briefly the countercurrent multiplier system and what it has to do with filtrate flow of the descending loop of Henle.

Answer 25

The descending loop of Henle begins in the adrenal cortex and ends deep in the adrenal medulla and begins after the PCT. The descending loop of Henle is only permeable to water. Blood osmolarity in the cortex is isotonic, blood osmolarity varies the deeper you go into the medulla from isotonic (trying to excrete water) to hypertonic (trying to conserve water).

The countercurrent multiplier is a system where the vasa recta and the nephron run counter to each other. This ensures that they don’t reach ionic equilibrium, as they would if the vasa recta and nephron ran in the same direction. The countercurrent multiplier system ensures that the filtrate is constantly being exposed to hypertonic blood allowing for maximum reabsorption of water.

Question 26

What is the ascending loop of Henle, where is it located, describe the change in permeability from the descending loop of Henle, describe the physiological change that occurs in the ascending loop of Henle.

Answer 26

The ascending loop of Henle is only permeable to salts. The ascending loop of Henle become thicker and is known as the diluting segment. It is thicker because of larger cells that contain mitochondria that allow the reabsorption of sodium and chloride by active transport. The ascending loop of Henle is the only part of the nephron that can produce urine that is more diluted than the blood.

Question 27

What is the distal convoluted tubule (DCT), where is it located, what hormone does the DCT primarily respond to, what’s the response?

Answer 27

The DCT is a portion of the nephron located in the adrenal cortex. The DCT responds to aldosterone which promotes sodium reabsorption (and promotes excretion of K and H). The DCT also secretes NH3 (blood to filtrate). Similar to PCT regarding salt reabsorption (and thus water) and waste product excretion.

Question 28

What is the collecting duct, where is it located, what hormone(s) is the collecting duct responsive to, what is the primary function of the collecting duct?

Answer 28

The collecting duct is the final duct in the nephron that ultimately leads to the renal pelvis and therefor the ureter. The collecting duct begins in the cortex and exits the medulla. The collecting ducts primary duty is to fine tune the reabsorption of water and is therefore highly permeable to water. The collecting duct however has variable permeability that is governed by aldosterone (increasing sodium reabsorption and therefor water) and ADH (responding to high blood osmolarity and thus causing reabsorption of water). Anything that is not reabsorbed by the collecting duct will ultimately be excreted, the collecting duct is the point of no return.

The fluid carried by the collecting duct is mostly urea, uric acid, excess ions (Na, K, Mg, Ca).

Question 29

What is the difference between osmotic pressure and oncotic pressure?

Answer 29

Osmotic pressure is the “sucking” pressure that draws water into vasculature caused by dissolved particles.

Oncotic pressure is the osmotic pressure that is attributable to dissolved proteins specifically.

Question 30

What is the bicarbonate buffer system, and how do the kidneys utilize this system? What happens when pH is low? High?

Answer 30

The bicarbonate buffer system is the major regulator of blood pH. The equation is:

CO2 + H2O - H2CO3 - H+ + HCO3-

The respiratory system utilizes this system, as does the excretory system. The kidneys may selectively increase or decrease excretion and reabsorption of H+ or bicarbonate (HCO3-) to help balance the pH of the blood.

If pH is too high, kidneys can excrete bicarbonate and reabsorb H+ to lower pH. The respiratory system will encourage slower respiration, increasing CO2 and thus H+ ions, shifting the buffer to the right.

If pH is too low, the kidneys can excrete H+ ions and reabsorb bicarbonate increase pH. The repertory system can encourage higher respiration, decreasing CO2, shifting the buffer system to the left increasing pH.

Question 31

What are the three layers of the skin?

Answer 31

The three layers of the skin are the hypodermis (subcutaneous layer), the dermis, and the epidermis.

Question 32

What germ layer does the skin come from?

Answer 32

The skin comes from then ectoderm.

Question 33

What are the five layers of the epidermis?

Answer 33

The five layers of the epidermis are (Come, Let’s Get SunBurned)

Stratum Corneum (horny cell)
Stratum Lucidum
Stratum Granulosum (granular)
Stratum Spinosum (squamous)
Stratum Basale (basal)

Question 34

What is special about the stratum basale?

Answer 34

The stratum basale contain stem cells and is responsible for proliferation of keratinocytes. The stratum basale is also the site of melanocytes, which produce melanin.

Keratinocytes produce keratin and are the predominant cells of the skin.

Question 35

What is special about the stratum spinosum?

Answer 35

The stratum spinosum is where the cells become connected to each other and is also the site of Langerhans cells, which are special macrophages that reside within the stratum spinosum. These cells are capable of presenting antigens to T cells in order to activate the immune system.

Spinosum - Langerhan- macrophage- antigens- T cells.

Question 36

What is special about the stratum granulosum (granular cell layer)?

Answer 36

In the stratum granulosum, the keratinocytes die and lose their nuclei.

Question 37

What is special about the stratum lucidum?

Answer 37

The stratum lucidum is only present in thick, hairless skin such as the skin on the sole of the foot or on the palms, and is nearly transparent.

Question 38

What is special about the stratum corneum (horny cell layer)?

Answer 38

The stratum corneum contains up to several dozen flattened keratinocytes, forming a barrier that prevents invasion by pathogens and helps prevent loss of fluid and salt.

Interesting. The ability of the skin to prevent fluid loss is very important in cases such as burns or large losses of skin as dehydration of the tissue became a real threat to survival.

Question 39

What are the main cells of the epidermis (not the main layers. The main CELLS)?

Answer 39

The main cells of the epidermis are keratinocytes. Keratinocytes are the predominate cells of the skin that produce keratin.

Question 40

What is a callus?

Answer 40

A callus forms from excessive keratin deposition in areas of repeated strain due to friction.

Question 41

What are melanocytes, where are they derived (embryologically), and why are they important?

Answer 41

Melanocytes are a cell type derived from neural crest cells (derived from the ectoderm) and found in the stratum basale. Melanocytes produce melanin, a pigment that serves to protect the skin from DNA damage caused by UV radiation.

Question 42

What are Langerhan cells, where are they located, and what are they capable of doing?

Answer 42

Langerhan cells are located in the stratum spinosum (squamous cells) and are specialized macrophages capable of presenting antigens to T cells in order to activate the immune system.

Question 43

What are the two layers of the dermis, and what are some cells and corpuscles located near the dermis?

Answer 43

The two layers of the dermis are the papillary layer and the reticular layer.

Merkel cells are located in the dermis/epidermis junction and are sensory receptors responsible for deep pressure and texture sensation within the skin.

Other corpuscles and endings found in the dermis are Meissner’s corpuscles (light touch), Ruffini endings (stretch), and Pacinian corpuscles (deep pressure and vibration).

Question 44

Where is the papillary layer, what does it consist of, and what are some cells and corpuscles located near the dermis?

Answer 44

The papillary layer is the uppermost layer of the dermis and consists of loose connective tissue.

Merkel cells (deep pressure and texture), Meissner’s corpuscles (light touch), Ruffini endings (stretch), and Pacinian corpuscles (deep pressure and vibration).

Question 45

What is a corpuscle?

Answer 45

A corpuscle is a minute body or cell in an organism that is not aggregated into continuous tissue.

Question 46

Where is the reticular layer and what does it consist of?

Answer 46

The reticular layer is the deep layer of the dermis forming a thick layer of dense connective tissue that constitutes the bulk of the dermis. Collagen is the principal component of the dermis.

Question 47

What is collagen?

Answer 47

Collagen is a protein that provides structure and support to the body’s connective tissues, bones, muscles, tendons, ligaments, and organs.

Question 48

What are Merkel cells (discs)?

Answer 48

Merkel cells are specialized cells in the skin that are involved in touch sensation and are present at the epidermal-dermal junction.

Question 49

What the Meissner’s corpuscles and where are they located?

Answer 49

Meissner’s corpuscles are sensory organs in the skin which respond to light touch. Located in the dermal papillae (papillary layer of the dermis).

Question 50

What are the Ruffini endings and where are they located?

Answer 50

Ruffini endings are sensory organs located in the skin that respond to stretch. Located in the dermis papillae.

Question 51

What are Pacinian corpuscles and where are they located?

Answer 51

Pacinian corpuscles are sensory organs located in the skin and respond to deep pressure and pressure and vibration.

Question 52

What is the hypodermis, where, and what does it consist of?

Answer 52

The hypodermis is a layer of connective tissue containing fat and fibrous tissue that connects the skin to the rest of the body.

Question 53

How is thermoregulation achieved by the skin?

Answer 53

Thermoregulation is the skin is achieved through sweating, piloerection, vasodilation, and vasoconstriction.

Question 54

How does the body cool itself regarding the skin?

Answer 54

The body cools itself by the skin through sweating. Evaporation is an endergonic physical reaction that absorbs energy as heat from our blood causing evaporation and thus a cooling effect. The body will vasodilate to increases blood exposure to the skin increasing the effect of evaporative cooling.

Remember that the neurons that innervate the sweat glands are strange in that they are postsynaptic sympathetic neurons that are cholinergenic (whereas most all the other postsynaptic sympathetic neurons are norandrogenic).

Question 55

How does the body warm itself when cold?

Answer 55

The body will contract erector pili muscles causing piloerection (hairs standing on end) which helps trap a layer of heated air near the skin. The body will vasoconstrict the capillaries of the skin to limit the exposure of blood to low temperatures. The body will also shiver which requires a sizable amount of ATP. Fat helps insulate the body, white fat and brown fat.

Question 56

What is white fat and brown fat, and what purpose do they serve?

Answer 56

White fat is adipose tissue (white adipose tissue WAT) and is the most common fat found and stores excess calories as fat droplets. Two primary white fat storage areas are visceral and subcutaneous.

Brown fat is adipose tissue (brown adipose tissue BAT) primarily functions in thermoregulation. BAT has an inefficient electron transport chain which means more heat energy is released through metabolism, causing a warming effect.

Question 57

Why are the neurons that innervate sweat gland unusual?

Answer 57

The neurons that innervate the sweat glands are POSTGANGLIONIC sympathetic neurons that are cholonergenic (they release acetylcholine instead of epinephrine).

This is strange because most POSTGANGLIONIC sympathetic neurons are noradregenic (use norepinephrine).

All preganglionic and neurons in the autonomic nervous system and postganglionic neurons in the parasympathetic nervous system are cholinergenic.

Question 58

How does the skin help with osmolarity of the body?

Answer 58

The skin is relatively impermeable to water which prevents water loss and water entrance from and to the body. This becomes very important in cases such as burns or large losses of skin as dehydration of the tissue becomes a real threat to survival.