Homeostatic Regulation

Homeostatic loopsIntroduction to hormonesNegative feed back in the human body

Examples of homeostatic systems• The Stress Response• Water Regulation• Blood Sugar Regulation

The Outline

Intro to homeostatic loops

Examples:

ThermoregulationBlood glucoseCa++ RegulationOsmoregulation

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A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism.

Water-soluble hormones: Composed of amino acids and bind a receptor protein on the surface of the target cell.

This starts a signal cascade inside the cell and the signal is amplified.

A single molecule of epinepherine can cause conversion of glycogen into about one million molecules of glucose.

They can travel freely in the blood because they "like" water. However, they are repelled by lipid or fatty structures

Examples include: insulin, oxytocin, epinepherine

Steroid hormones:Receptors are located intracellularly within the cytoplasm of the target cell.

To bind their receptors, these hormones must cross the cell membrane. They can do so because they are lipid-soluble. Generally synthesized from cholesterol.

Example: testosterone or cortisol

Hormonal RegulationDesign a negative feedback loop(general)

Thyrotropin-releasing hormone (TRH) stimulates the release of TSH (thyroid-stimulating hormone) and prolactin from the anterior pituitary.

Thyroid-stimulating hormone is a hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body.

Thyroxin – Regulates Metabolism

The Stress Response

Hormonal RegulationDesign a negative feedback loop (cortisol)

Stress

Adrenaline (Epinephrine)stress hormones secreted from the adrenal glands, which sit above the kidneys.

Adrenaline primarily binds to receptors on the heart and heart vessels. This increases heart rate, force of muscle contraction and respiration. (Short term response)

Cortisol binds to receptors on the fat cells, liver and pancreas, which increases glucose levels available for muscles to use. It also temporarily inhibits other systems of the body, including digestion, growth, reproduction and the immune system. Long term cognitive effects.

Stress

http://vimeo.com/42572194

Water Regulation

• Water is expelled during respiration and is continually being moved through the skin to moderate temperature and flush the tissues of the skin

• Water is used for metabolic processes

• Lack of water = decreased organ function and toxin build up

• Common signs of dehydration: dark urine, afternoon fatigue, heartburn, dry skin, acne, headaches and constipation

• Effects on concentration and mood

Water Regulation

• Osmotic pressure builds up in blood• Osmoreceptors in hypothalamus sense increased osmotic

pressure and send signals to the pituitary gland to realease ADH into blood stream

• ADH affects distal tubule and collecting duct allowing more water to be reabsorbed into blood

Water Regulation

How do you detect a need for fluids?

Substance % Reabsorbed

Water 99.4%

Na 99.4%

K 93.3%

HCO3 100%

Glucose 100%

Urea 53%

Inulin 0%

As the filtrate passes down the nephron most of it is reabsorbed into the blood

Reabsorption & secretion:

Data from: William Ganong. Review of Medical Physiology. 1999.

How do the kidneys do it??

Nephron

Nephron: Primary functional unit of the kidney.

Its microscopic tubular structure is responsible for the filtration of

wasteful substances and reabsorption of valuable

substances in the blood to create urine.

Steps necessary to create URINE

1. Glomerular Filtration

2. Tubular reabsorption

3. Tubular secretion

4. Water reabsorption

Glomerular FiltrationTakes place in renal corpuscle

Glomerulus Bowman’s Capsule

1. Glomerular Filtration

• Glomerulus: Bundle of fine capillaries in which blood first enters the kidneys– Water and other small substances are forced into

the Bowman’s Capsule• Water• Salts/ions (Na+ & K+)• Glucose• Waste product: Urea

– Formed to rid of the toxic ammonia – byproduct of metabolic process of liver from amino acids

Glomerular Filtrate

1. Glomerular Filtration

Factors affecting Glomerular Filtration

① Permeability of glomerulus ② Blood Pressure

– 4 times higher blood pressure than any other capillary• Source of the force used for filtration.

1. Glomerular Filtration

Takes place in the Proximal Tubule Between the Bowman’s Capsule and Distal Tubule • Many of the substances filtered into the nephron are removed

during tubular reabsorption– Accounts for 65% of filtrate

– Substances can exit in 3 ways:① Passive transport – Diffusion② Active Transport③ Osmosis

2. Tubular reabsorption

• Active transport– Salts (Na+ & K+)– Glucose – Amino acids

• Passive Transport– Negatively charged ions (Cl- & HCO3

-)a. Electrical attraction with cations

• Osmosis– Water is reabsorbed

Reabsorption in Proximal Tubule

2. Tubular reabsorption

The proximal tubule reabsorbs: • between 40 and 60% of the glomerular ultrafiltrate• Glucose and amino acids • 70% of the filtered K+ and 75% of the bicarbonate (HCO3).

The cytoplasm of the cells that make up the proximal tubule is densely packed with mitochondria necessary to supply the energy for the active transport of sodium ions out of the proximal tubule. Water passively follows the sodium out of the cell along its concentration gradient.

2. Tubular reabsorption

Reabsorption in Loop of Henle

Loop of Henle

Thinner, “U” shaped portion of the proximal tubule that extends into the renal medulla • Descending limb – Permeable to water

– Enters into the salty medulla– H2O exits into the capillaries along its gradient - Osmosis– Consequently, the concentration of Na+ inside increases

• Ascending limb – Impermeable to water– Thin portion

• Chloride ions are actively transported out• Sodium cations diffuse out of nephrons due to attractive forces

– Thick portion• Sodium cations are actively transported out into the medulla

Importance of Na+

removal from Nephrons

① Replenishes the salty environment of medulla

② Makes filtrate less concentrated than surrounding tissues and blood

No sodium ions ever enter the capillaries during tubular reabsorption

3. Tubular Secretion

Takes place in the Distal Tubule Immediately prior to collecting duct

• Two primary secretions:

①Potassium ions (K+)

②Hydrogen ions (H+)– Regulate blood pH by

the removal of H+

4. Water reabsorption

Takes place in the Collecting duct Final portion of nephron

• As in the proximal tubule, water exits the filtrate via osmosis– High concentration of salt in the

medulla• Permeability of collecting duct can

alter based on water levels in blood:– Enough water: less permeable –

less H2O returns to blood– Dehydration: more permeable–

more H2O returns to blood

• Only 1% of the initial distillate from glomerulus– 99% is re-absorbed by blood

• Total of 180 Liters of distillate enter the nephrons per day– 178.2 L return to blood– 1.8 L is removed via urine

Urine has been created! … but what is it?

Reabsorption & secretion:

• A few substances are secreted from the blood to the nephron

• Reabsorption and secretion are energy intensive- the kidney is one of the most metabolically active organs in the body

• Filtering substances into the tubules and then reabsorbing nearly 100% of them, using energy, may seem to be a very wastefull process, but it allows the body to quickly remove many toxic substances from the blood (they are usually not reabsorbed)

Net Process: Amt in Urine = Amt Filtered - Amt Reabsorbed + Amt Secreted

Glomerular Filtration is Easy to Measure From Inulin or Creatinine

Clearance

Functions of the Excretory System1. Excretion of Metabolic Wastes -Mainly nitrogen containing wastes.2. Maintenance of Water- Salt Balance -Indirectly regulates blood volumes.3. Maintenance of Acid – Base Balance -Carbonic acid buffer system.4. Secretion of Hormones -Calcitriol (calcium absorption) + erythropoietin

(production of red blood cells).

Blood Sugar Regulation

Blood sugar regulation

• Too HIGH• Insulin secreted from β cells in the

Islet Langerhan• Liver stores glucose as glycogen• Muscles cells store glycogen and

build protein• Adipose tissue uses glucose to

build fat

• TOO Low• α cells (Islets of Langerhan)• Liver breaks down glycogen to

glucose• Adipose tissue breaks down fat

Figures to know and love:

Figures: 9.13, 9.16, 9.18,9.20,10.4,10.6, 10.11, 10.12

Table 10.3