BI111 Lecture Notes - Lecture 14: Distal Convoluted Tubule, Juxtaglomerular Apparatus, Cyclic Adenosine Monophosphate
Biology: Urinary system unit
Homeostasis: Body’s ability to maintain stable conditions
Exp. Thermoregulation: maintenance of specific body temperatures that is controlled by the
hypothalamus of the brain. (37 degrees)
Positive feedback: results in amplification or growth of the output signal
Negative feedback: system responds in an opposite direction to the perturbation.
Endotherms (like humans) able to maintain a constant body temperature
Ectotherms (like lizards) depend on the exterior environment to control the metabolism
Heat stress:
• Sweat glands release sweat that cools as it evaporates on the surface of skin
• At same time, blood vessels dilate to allow blood to cool down near the surface, then more to the
internal organs to cools them
• Aka, sweating cools you down because evaporation absorbs energy- loss of heat
Cold stress:
• Nerves trigger contractions of smooth muscles to restrict arteries to reduce heat loss
• Hair follicles stand on the end (goosebumps) to trap warm air near the skin
• Skeletal muscles start shivering
• When your exposed to the cold for a long time, the body will divert blood to the brain and other
vital organs
The urinary system:
Kidneys:
o Help control water levels in the body
o Help balance blood pH
o Waste products removed- exp alcohols, toxins and heavy metals
o Is used as a filter
➢ The liver detoxifies most dangerous compounds in the body, then the kidneys will eliminate the
detoxified waste from the body
➢ Proteins are deaminated by liver creating ammonia- toxic
o Combined with carbon dioxide, ammonia can form urea and uric acid (safer to store)
Structure of urinary system
Blood is carried to and from the kidneys via renal arteries and veins
Wastes are carried from the kidneys to the bladder through ureters. The urethra carried urine from
the bladder to remove wastes
Kidney has 3 basic structures
o Cortex- outer layer of connective tissue
o Medulla- inner layer of connective tissue
o Renal pelvis- joins the kidney to the ureter
*High blood pressure= produces more urine
*You can’t have to much water in the blood because it dilutes the blood, thins out and increases blood
pressure.
The Nephron system
Inside the kidneys, are millions of tubules called nephrons; where filtration of the blood begins
Renal artery branches into small afferent arterioles that bring blood to a cluster of capillaries called
glomerulus (an artery, NOT PART OF URINARY SYSTEM)
Wastes that need to be filtered enter the Bowman’s capsule that surround the glomerulus
*Bowman’s capsule is the start to the urinary system
The wastes that are filtered, are collected by bowman’s capsule
Blood then continues to capillaries that wrap around the tubules beyond the Bowman’s capsule: 1.
Proximal tubule 2. Loop of Henle 3. Distal tubule
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Final collecting ducts eventually lead to the ureters
The formation of Urine
1. Filtration
• In glomerulus
• Movement of blood at high blood pressure forces dissolved waste materials out of the
capillaries, into the bowman’s capsule
2. Reabsorption
• 20% of blood entering the kidneys is filtered into nephrons
• Most of the water that passes though the nephron is reabsorbed; otherwise almost 100ml of
urine would be formed every minute
• Movement of ions (such as Na+, Cl-, and HCO-3) help control movement of water (osmosis) aka
water follows because of osmosis
• Salt makes blood more concentrated- water goes to a more concentrated area, and takes water
out of urine
• Active and passive transport (higher to lower concentration) are used to complete the process
• Final reabsorption of water allows a concentration of the urine
Proximal tubule: reabsorption of H2O, HCO3-, NaCl, glucose, vitamins from filtrate to blood
o Helps control pH of blood/urine with HCO3
Descending loope of Henle: water is passively lost from urine (filtrate) going back into blood
(rehydrating)
o This concentrates the urine
Ascending Loope of Henle: active and passive loss of NaCl from urine
3. Secretion:
• Distal tubule→ reabsorption of H2O, HCO3-, NaCl from filtrate to blood. This regulates blood salt
and pH levels.
o Not a lot of reabsorption of water
• Collecting ducts: H2O, NaCl, urea, minerals are reabsorbed. This completes urine formation.
Keeping Water Balance
• Urinary output is the primary method of regulating body water levels. The endocrine and nervous
system
• ADH (antidiuretic hormone)- causes water retention in the kidney
o The release of ADH causes the kidney to produce a more concentrated urine, meaning less
water is needed
o Is produced in the hypothalamus of the brain
• There are specialized osmorceptors in the hypothalamus that can detect osmotic pressure
• When hypothalamus begins to shrink from high osmotic pressure, then a thirst is triggered
o Drinking water dilutes the blood and reduces thirst
*High osmotic pressure→concentrated, less water, dehydrated
• Proximal tubule is responsible for most of the reabsorption of water
• *ADH makes the distal tubule and collecting duct more permeable to water
• Since there is a high concentration of salt around the tubules, this draws more water out of the
ducts- this concentrates the urine
• Kidneys regulates blood pressure
• Decrease of water in the blood means loss of blood pressure
o Receptors in the juxtaglomerular apparatus detect low blood pressure
o This triggers the release of renin which converts angiotensinogen into the active hormone
angiotensin
o Angiotensin constricts blood vessels, and triggers the release of aldosterone
▪ Aldosterone helps reabsorb more Na+ from the distal tubule
• The movement of water will follow the movement of Na+
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• The pH of blood is regulated in the kidney by controlling the bicarbonate- carbon dioxide reactions
in the blood
Hormones and the endocrine system
Hormones: chemicals released by cells, have an impact on cells in other parts of the body.
o Help speed up, or slow down body functions.
o The name of the hormone is often related to its active site.
o Not every hormone affects every cell; some cells may only recognize specific hormones.
o Endocrine glands: release hormones into the blood for transport throughout the body.
o Some common hormones that do not have a specific target tissue are:
o Growth hormone – produced in pituitary gland
o Insulin – produced in pancreas
o Epinephrine – produced in adrenal gland cells.
• There are two major classes of hormones
1. Steroid hormones
➢ Made from a lipid (like cholesterol) that is fat (not water) soluble.
➢ Can pass through cell membrane, and binds to a receptor molecule inside the cell to
carry out a function.
➢ E.g. Sex hormones and cortisol.
2. Protein hormones
➢ Chains of amino acids.
➢ Bind to receptors on the exterior cell membrane.
➢ Hormone-receptor complex: activate/create an enzyme or secondary messenger (ex.
cAMP) inside the cell.
➢ E.g. Insulin and Growth Hormone
• The endocrine system works with the nervous system to help control and coordinate all organs and
tissues in the body.
• The endocrine system provides control over a long period of time (minutes to years).
• Some of the most important tissues involved in the endocrine system are:
➢ Hypothalamus
➢ Thyroid/parathyroid gland
• Pituitary gland
o Master gland that controls most endocrine glands.
o Attached to the hypothalamus of brain, controls the release of pituitary hormones.
• Posterior lobe releases hormones, like Antidiuretic hormone and oxytocin, produced in the
hypothalamus.
• Anterior lobe produces hormones like growth hormone(GH), LH, FSH, ACTH. Also regulated by the
hypothalamus.
Hormones that affect blood sugar
• The human body needs glucose as a fuel for cellular respiration.
• Every time food is digested, the glucose enters the blood where it can be distributed throughout the
body.
• Blood glucose levels are strictly maintained within a specific range of approximately 0.7g/L –
1.1g/L.
• An individual whose blood sugar is more than 1.1g/L is termed hyperglycemic.
• While an individual whose blood sugar is below 0.7g/L is termed hypoglycemic.
• Once blood glucose levels fall outside this range, the body will begin to respond to return the
glucose levels to normal.
• The pancreas is the organ responsible for the endocrine response to blood sugar.
• When blood sugar is higher than normal, the pancreas releases the hormone insulin from beta cells
in the islets of Langerhans.
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Document Summary
Thermoregulation: maintenance of specific body temperatures that is controlled by the. Homeostasis: body"s ability to maintain stable conditions hypothalamus of the brain. (37 degrees) Positive feedback: results in amplification or growth of the output signal. Negative feedback: system responds in an opposite direction to the perturbation. Endotherms (like humans) able to maintain a constant body temperature. Ectotherms (like lizards) depend on the exterior environment to control the metabolism. Kidneys: help control water levels in the body, help balance blood ph, waste products removed- exp alcohols, toxins and heavy metals. The liver detoxifies most dangerous compounds in the body, then the kidneys will eliminate the detoxified waste from the body. Proteins are deaminated by liver creating ammonia- toxic: combined with carbon dioxide, ammonia can form urea and uric acid (safer to store) Blood is carried to and from the kidneys via renal arteries and veins. Wastes are carried from the kidneys to the bladder through ureters.
