Chapter 11 - Homeostasis Flashcards
Homeostasis (definition and examples)
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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
Osmoregulation
Maintenance of water and solute concentrations
Thermoregulation
Maintenance of a constant internal body temperature
Why is homeostasis critical?
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
Kidney: functions
- Excrete waste products (i.e., urea, uric acid, ammonia, phosphate)
- Maintain homeostasis: fluid volume; solute composition (Osmoregulation)
- Control plasma pH
Kidney: diagram
Kidney Cortex (compnents)
Outermost layer of the kidney. Consists of renal corpuscle (glomerulus & Bowman’s capsule), Proximal tubule, and Distal Tubule. Collecting duct straddles cortex/medulla.
Medulla
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.
Flow of blood through kidney
Arteries (Somatic) → Afferent arteriole → Glomerulus → Efferent Arteriole → Vasa Recta (if medullary nephron) → Arteries (Somatic)
Nephron
(and components, in order)
Functional unit of kidney:
Renal corpuscle → proximal tubule → loop of Henle → distal tubule → collecting duct
Renal corpuscle
Region of nephron (kidney) where filtration occurs. Made up of glomerulus and Bowman’s capsule. Located in cortex.
Filtrate
The material that passes from the blood vesels into Bowman’s capsule
Proximal tubule
Region of nephron (kidney) where reabsorption (water, glucose, proteins, etc.) and secretion (drugs, toxins, etc.) occurs. Located in cortex.
Distal tubule
Region of nephron (kidney) where osmolarity is lowered. In presence of ADH, water flows out of tubule, concentrating filtrate. Located in cortex.
Collecting duct
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.
Juxaglomerular apparatus
Monitors filtrate pressure in the distal tubule.
Vasa recta
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.
Loop of Henle
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.
How does plasma enter the glomerulus of the kidney for filtration?
Hydrostatic pressure forces plasma through sieve-like “fenestrations” (which keep out blood cells and large proteins).
What are the three fundamental mechanisms used by the kidney to maintain homeostasis and osmoregulation.
(These determine urinary excretion rate)
Urinary excretion rate (UER) is determined by:
- Filtration
- Secretion
- Reabsorption
UER = F – R + S
Filtration (definition and locations in kidney)
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.
Secretion (definition and locations in kidney)
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.
Reabsorption (definition and locations in kidney)
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.
Kidney filtration and reabsorption sites (diagram)
What two physical principles of solute movement work in concert in the nephron to allow for selective reabsorption and excretion? What is this called?
- 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.
Filtration, Secretion, and Reabsortpion in the Nephron (diagram)
Filtrate flow (list)
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
How is water moved into and out of the kidney?
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.
What does the final concentration of urine depend on?
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.
Renin
Enzyme secreted by granular cells of juxtaglomerular apparatus. activates angiotensin, which stimulates the adrenal cortex to secrete aldosterone.
Aldosterone: effect on kidney?
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.
Aldosterone: regulation
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.
ADH: effect on kidney?
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.
ADH: generation and regulation
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.
Compare the mechanisms of action of aldosterone and ADH in regulating osmolarity.
- 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.
What three compunds should always be absent from healthy urine?
The presence of any of these molecules in urine indicates kidney pathology:
- Blood - too large to filter (glomerular pathology)
- Protein - too large to filter (glomerular pathology)
- Glucose - typically reabsorbed (tubular pathology)
What are the two most important liver functions in maintaining homeostasis?
- Blood glucose regulation
- elimination of nitrogenous waste through urea
Gluconeogenesis
A process in the liver by which glucose is produced using by-products from glycolysis, lipids, or fats.
Glycogen
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.
How do nitrogenous waste products arise, and how are they dealt with?
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.
Liver functions (Lots!)
- 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
Large intestine: main functions
- Water absorption
- Electrolyte absorption
E. coli in the large intestine: function
Symbiotic relationship. Bacteria get our “leftovers.” They produce certain vitamins for us (K, B₁₂, thamin, riboflavin).
Skin: functions
- Thermoregulation (reduce temp through sweat, but mostly radiation; increase temp by shunting blood away from skin capillaries or erecting hair to trap warm air)
- Protection (physical barrier)
- Environmental sensory input (temp, pressure, pain, touch)
- Excretion (water, salt - this is independent of sweating)
- Immunity (specialized epidermal cells part of immune system)
- Blood reservoir (dermis)
- Vitamin D synthesis
Skin: components
- Epidermis
- Dermis
- Subcutaneous tissue
Epidermis: composition, cell types
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:
- Keratinocytes (top layer; produce kertain to waterproof skin)
- Melanocytes (transfer melanin pigment to keratinocytes)
- Langerhans cells (interact w/helper T-cells)
- Merkel cells (deepest layer; attach to sensory neurons; help w/touch)
Dermis
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.
Hypodermis
Subcutaneous skin tissue (under dermis). The fat of this layer helps insulate body. Serves to bind the dermis to the body.
Integumentary system
Skin, hair, nails, glands, some nerve endings form this system.
Skin: Diagram
Epidermis: sublayers and function
Serves as a protective barrier against microbial attack. Derived from the ectoderm.
- Stratum basalis
- stratum spinosum
- stratum granulosum
- stratum lucidum
- stratum corneum
