Homeostatsis

Question 1

What is homeostasis?

Answer 1

The physiological state of the body in which the internal physical and chemical conditions are maintained within an acceptable range that is suitable for biological processes.

Question 2

Terminology(Stimulus )

Answer 2

the trigger for a change in a homeostatic control mechanism (eg. too hot, too cold, high blood pressure, etc)

Question 3

Terminology(Sensor )

Answer 3

a specialized cell or group of nerve endings that responds to sensory stimuli. Or a site on a cell that binds with substances such as hormones, antigens, drugs, or neurotransmitters.

Question 4

Terminology(Integrator )

Answer 4

most commonly an organ (eg. the brain, endocrine glands) which receives information. Compares conditions with optimal functioning conditions (Set Points). Then generates control signal information (eg. nerve impulses, hormones)

Question 5

Terminology(Effector )

Answer 5

A muscle, gland, or organ capable of responding to control signal.

Question 6

Regulation by Feedback(negative feedback)

Answer 6

• These mechanisms change the variable back to its original state or “ideal value”
• Almost all homeostatic control mechanisms are negative feedback mechanisms.

Question 7

Regulation by Feedback( Positive Feedback)

Answer 7

• In a positive feedback system, the output enhances the original stimulus.

💡 Just remember that positive feedback mechanisms enhance the original stimulus and the negative feedback mechanisms that inhibit it

Question 8

Regulation is Controlled by(Nervous System)

Answer 8

• Electrical

- Enables body to quickly adjust

Question 9

Regulation is Controlled by(Endocrine System)

Answer 9

• Chemical

- Maintains control over longer duration

Question 10

Some Examples of What Needs to Be Regulated

Answer 10

• Body Temperature
• Blood Pressure
• Blood pH
• Blood Sugar
• Osmoregulation - balance between water and dissolved materials

Question 11

Excretory System(The Mammalian Kidney)

Answer 11

• The kidneys are bean-shaped excretory organs in vertebrates.
• Part of the urinary system, kidneys filters wastes (especially urea) from the blood and excrete them, along with water, as urine.
• The medical field that studies the kidneys and diseases affecting the kidney is called nephrology, from the greek name for the kidney.
• The adjective meaning “kidney-related” is renal.

Question 12

Excretory System( Location)

Answer 12

• In the humans, the kidneys are located in the posterior part of the abdomen.
• There is one on each side of the spine; the right kidney sits just below the liver, the right kidney sits right below the diaphragm and adjacent to the spleen.
• Above each kidney is an adrenal gland (also called the suprarenal gland).
• The kidneys are retroperitoneal, which means they lie behind the peritoneum, the lining of the abdominal cavity.
• , and the right kidney usually lies slightly lower than the left in order to accomodate the liver.
• The upper parts of the kidneys are partially protected by the eleventh and twelfth ribs, and each whole kidney is surrounded by two layers of fat (the perirenal fat and the pararenal fat) which help to cushion it.

Question 13

Excretory System(Structure)

Answer 13

• In a normal human adult, each kidney is about 11 cm long about 5 cm thick, weighing 150 grams.
• The kidneys are “bean-shaped” organs and have a concave side facing inwards (medially).
• On this medial aspect of each kidney is an opening, called the hilum, which admits the renal artery, the renal vein, nerves, and the ureter.
• The outermost portion of the kidney is called the renal cortex, which sits directly beneath the kidney’s loose connective tissue capsule.
• Deep to the cortex lies the renal medulla which is divided into 10-20 renal pyramids in humans.
• Each pyramid together with the associated overlying cortex forms a renal lobe.
• The tip of each pyramid (called a papilla) empties into a calyx, and the calyces empty into the renal pelvis.The pelvis transmits urine to the urinary bladder via the ureter.

Question 14

Blood Supply

Answer 14

• Each kidney receives its blood supply from a renal artery, two of which branch from the abdominal aorta.- Upon entering the hilum of the kidney, the renal artery divides into smaller arteries.
• Branching off these arteries are the afferent arterioless upplying the glomerular capillaries, which drain into efferent arterioles.
• Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the cortex.
• Blood from these capillaries collects in renal venules and leaves the kidney via the renal vein.

Question 15

Nephron

Answer 15

• The basic functional unit of the kidney is the nephron.
• There are more than a million in each normal adult human kidney.
• Nephrons regulate water and soluble matter (especially electrolytes) in the body by first filtering the blood, then reabsorbing some necessary fluid and molecules while secreting other, unneeded molecules.
• Reabsorption and secretion are accomplished with both cotransport and countertransport mechanisms established in the nephrons and associated collecting ducts.

Question 16

Urine Formation(The Glomerulus)

Answer 16

• The glomerulus is the main filter of the nephron and is located within the Bowman’s capsule.
• The glomerulus resembles a twisted mass of tiny tubes through which the blood passes.
• The glomerulus is semipermeable, allowing water and soluble wastes to pass through and be excreted out of the Bowman’s capsule as urine.
• The filtered blood passes out of the glomerulus into the efferent arteriole.

Question 17

Urine Formation(bowman’s Capsule)

Answer 17

• The Bowman’s capsule contains the primary filtering device of the nephron, the glomerulus.
• Blood is transported into the Bowman’s capsule from the afferent arteriole (branching off of the interlobular artery).
• Within the capsule, the blood is filtered through the glomerulus and then passes out via the efferent arteriole.
• The filtered water and aqueous wastes are passed out of the Bowman’s capsule into the proximal convoluted tubule.

Question 18

Urine Formation(Reabsorption and Secretion)

Answer 18

• Most of the water and dissolved solutes that enter the glomerular filtrate must be returned to the blood.
• Reabsorption of glucose and amino acids, is driven by active transport carriers.
• Secretion of waste products involves transport across capillary membranes and kidney tubules.

Question 19

Proximal Convoluted Tubule

Answer 19

• The glomerular filtrate passes first into the proximal convolute
  tubule.
• Energy dependent mechanisms reabsorb all of the following
  constituents:
  
  • glucose
  • amino acids
  • potassium
  • sodium - about 80% reabsorbed
  • bicarbonate
  • active secretion also transports other compounds e.g. penicillins,
• There is passive reabsorption of water and chloride.
• The solutes are absorbed isotonically, in that the osmotic potential of
  the fluid leaving the proximal tubule is the same as that of the initial
  glomerular filtrate.
• However, glucose, amino acids, inorganic phosphate, and some
  other solutes are reabsorbed via secondary active transport through
  cotransport channels driven by the sodium gradient out of the
  nephron.

Question 20

Loop of Henle

Answer 20

• The loop of Henle (sometimes known as the nephron loop) is a U-shaped tube that consists of a descending limb and ascending limb.
• It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medula, and then returns to the cortex to empty into the distal convoluted tubule.
• Its primary role is to concentrate that salt in the interstitium, the tissue surrounding loop.

Question 21

Descending Limb

Answer 21

• It is permeable to water but completely impermeable to salt.
• As the filtrate descends deeper into the hypertonic, as the filtrate descends deeper into the hypertonic interstitium of the renal medulla, water flows freely out of the descending limb by osmosis until the tonicity of the filtrate and interstitium equilibrate.
• Longer descending limbs allow more time for water to flow out of the filtrate

Question 22

Ascending Limb

Answer 22

• Unlike the descending limb, the ascending limb of the Henle’s loop is impermeable to water
• The ascending limb actually pumps sodium out of the filtrate, generating the hypertonic interstitium that drives counter-current exchange.
• In passing through the ascending limb, the filtrate grows hypotonic since it has lost much of its sodium content.
• This hypotonic filtrate is passed to the distal convoluted tubule in the renal cortex.

Question 23

Distal Convoluted Tubule

Answer 23

• The digital convoluted tubule is similar to the proximal convoluted tubule in structure and function
• Cells lining the tubule have numerous mitochondria, enabling active transport to take place by the energy supplied by ATP.
• Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system
• In the presence of parathyroid hormone, the distal convoluted tubule reabsorbs more calcium and excretes more phosphate.
• When aldosterone is present, “more sodium is reabsorbed and more potassium excreted.
• The tubule also secretes hydrogen and ammonium to regulate pH.
• After travelling the length of the distal convoluted tubule, only 3% of water remains, and the water remains, and the remaining salt content is negligible.

Question 24

Collecting Duct

Answer 24

• Each distal convoluted tubule delivers its filtrate to a system of collecting
  ducts. Each distal convoluted tubule delivers its filtrate to a system of collecting
  ducts, the first segment of which is the connecting tubule.
• The collecting duct system begins in the renal cortex and extends deep into the
  medulla.
• As the urine travels down the collecting duct system, it passes by the medullary
  interstitium which has a high sodium concentration as a result of the loop of
  Henle’s countercurrent multiplier system.
• Though the collecting duct is normally impermeable to water, it becomes
  permeable in the presence of antidiuretic hormone (ADH).
• As much as three-fourths of the water from urine can be reabsorbed as it leaves
  the collecting duct by osmosis.
• Thus the levels of ADH determine whether urine will be concentrated or dilute.
• Dehydration results in an increase in ADH, while water sufficiency results in low
  ADH allowing for diluted urine.
• Lower portions of the collecting duct are also permeable to urea Lower portions
  of the collecting duct are also permeable to urea, allowing some of it to enter
  the medulla of the kidney, thus maintaining its high ion concentration (which is
  very important for the nephron).
• Urine leaves the medullary collecting ducts through the renal papilla, emptying
  into the renal calyces, the renal pelvis, and finally into the bladderUrine leaves
  the medullary collecting ducts through the renal papilla, emptying into the renal
  calyces, the renal pelvis, and finally into the bladder via the ureter.

Question 25

Regulation of Kidneys Antidiuretic Hormone (ADH)

Answer 25

• ADH is polypeptide hormone secreted by the posterior pituitary gland .
• Its principal action is to regulate the amount of water excreted by the kidneys.
• ADH, known also as vasopressin, causes the kidneys to resorb water directly from the
  distal tubules, thus concentrating the salts and waste products in the liquid, which will eventually become urine.
• ADH secretion by the pituitary is regulated by neural connections from the hypothalamus, which is believed to monitor either the volume of blood passing through it or the concentration of water in the blood.
• Dehydration or body stress will raise ADH secretion and water will be retained.
• Alcohol inhibits ADH secretion.
• Failure of the pituitary to produce ADH results in diabetes insipidus.
• In pharmacological doses ADH acts as a vasoconstrictor. The structure and chemical
  synthesis of ADH was announced (1953) by Nobel laureate Vincent Du Vigneaud and others.

Question 26

Aldosterone

Answer 26

Aldosterone is a steroid hormone produced by the outer-section of the adrenal cortex in the adrenal gland to regulate sodium and potassium balance in the blood.

• It is synthesized from cholesterol by aldosterone synthase
• aldosterone acts by increasing sodium reabsorbtion from the distal tubule and the collecting duct