Endocrine Glands:

Hormones:

-Endocrine glands release hormones directly into the blood

-Hormones alter the activity of tissues that possess receptors to which the hormone can bind

-The plasma hormone concentration and the number of active receptor sites etermine the magnitued of the effect at the tissue level

1.) Concentration of hormone in the plasma

-rate of secretion of the hormone

-rate of removal of the hormone (metabolized or excreted)

-quantity of transport protein

-changes in plasma volume

2.) Number of active receptor sites

Receptor sites

-down regulation

-up regulation

-hormones affect only tissue with protein receptor sites specific to the hormone

--down regulation: a decrease in the number of active receptor sites

--up regulation: an increase in the number of active receptor sites

1.) Membrane Transport: activate carrier proteins of facillitated diffusion

2.) Stimulation of DNA to produce mRNA: mRNA carries code for specific protein synthesis in cytoplasm

3.) Secondary Messengers (cyclic AMP and Calcium)

-the binding of some hormones to cell membrane causes activation of carrier molecules located in or near membrane

-carrier molecules increase movement of substrate or ions to inside of cell

-EXAMPLE: Insulin binding with receptor in membrane activates glucose transport molecules which bind glucose and diffuse with in inside of cell

anterior lobe: adrenocorticotrophic hormone (ACTH), follicle stimulating hormone (FSH), luteinizing hormone (LH), growth hormone (GH), thyroid stimulating hormone (TSH), prolactin, beta-endorphin

posteror lobe: oxytocin, antidiuretic hormone (ADH) or vasopressin

Pituitary Glands (hormones definitions)

ACTH, TSH, GH, ADH

anterior lobe

1. ACTH: stimulates the synthesis and release of cortisol from the adrenal cortex
2. TSH: stimulates and synthesis and release of triiodothyronine (T3) and thyroxine (T4) from the thyroid gland
3. GH: promotes growth in almost all cells in the body by stimulating somatomedins which mediate growth responses; increase gluconeogenesis in liver, decreases glucose uptake by adipose cells

posterior lobe

1. ADH: promotes reabsorption of water by kidneys and therefore acts to increase blood pressure

1. triiodothyronine (T3): regulates body metabolic rate, important in bone growth; relative for fast acting; less prevalent
2. thyroxine (T4): regulates body metabolic rate, important in bone growth, relatively slow acting; more prevalent
3. calcitonin: minor role in calcium regulation; blocks the release of calcium from bone
4. parathyroid hormone: primary hormone involved in regulation of plasma calcium; stimulates release of calcium from bone

-actually two glands, the adrenal medulla and the adrenal cortex

-is part of the sympathetic nervous system

-secretes two hormones responsible for the "flight or fight" response

1.)epinephrine: increases HR, O2 consumption, and glycogenesis

2.)norepinephrine: increases BP, constricts blood vessels

1.)Cortisol: promostes breakdown of tissue protein, stimulates mobilization of FA, stimulates liver production of glucose, block entrance of glucose into tissues, has inflammatory and anti-immune functions

2.)Aldosterone: regulates sodiume reabsorption and potassium secretion by the kidneys; helps control plasma volume and blood pressure

1. Insulin: secreted from beta cells of islets of Langerhans; stimulates uptake by tissues of nutrients (glucose and amino acids) **Reduce plasma glucose levels

2. Glucagon: secreted from alpha cells of islets of Langerhans; stimulates mobilization of glucose from liver and FFA from adipose tissue  **Increase plasma glucose levels

3. Somatostatin: secreated by the delta cells of islets of Langerhans; regulates insulin secretion and rate of absorption in GI tract

• Glucose is taken up 7 to 20 times faster during exercise (depending on intensity of exercise)
• During intense exercise, FA oxidation cannot compensate for CHO usage
• Performing prolonged moderate to intense exercise is dependent upon maintaining plasma glucose

Blood Glucose Homeostasis During Exercise (4)

1. Mobilization of glucose from liver glycogen (glycogenolysis)

2. Mobilization of FFA from adipose tissue

3. Synthesis of new glucose from amino acids and glycerol (gluconeogenesis)

4. Inhibition of glucose uptake

• Increased concentrations of catecholamines (epinephrine and norepinepherine)
• Increased glucagon concentration due to actions of E and NE on alpha cells of pancreas
• Decreased insulin concentration due to actions of E and NE on beta cells of pancreas

1. Glycogenolysis is related to exercise intensity.  High intensity exercise results in greater and more rapid glycogen depletion.

2. Plasma epinephrine is a powerful stimulator of glycogenolysis.  High intensity exercise results in greater increases in plasma epinephrine.

Hormonal Responses Favoring Mobilization of FFA

**glycogen sparing**

1. increased cortisol concentration
2. increased growth hormone concentration
3. increased concentrations of catecholamines (E and NE)--response mediated by thyroxine
4. increased glucagon concentration
5. decreased insulin concentration

1. increased cortisol concentration

2. increased growth hormone concentration

3. increased E and NE concentrations

Slow acting:

-increased cortisol concentration (mobilizes tissue protein to yield amino acids)

-increased growth hormone concentration

Fast acting:

-increased glucagon concentration

-decreased insulin concentration

1. FFA mobilization decreases during heavy exercise

-this occurs despite persisting hormonal stimulation for FFA mobilization

2. Can be due to...

-high levels of lactate which promote resynthesis of triglycerides from FFA

-high levels of H inhibit lipase

-inadequate blood flow to adipose tissue

-insufficient transporter for FFA in plasma

1. Breakdown of fatty acids depends on a background level of CHO metabolism

2. Acetyl-CoA enters Kreb's cycle only by combining with oxaloacetic acid which is generated primarily by CHO catabolism

3. The degradation of fatty acid is dependent upon Krebs cycle activity; therefore, low Kreb's cycle activity means low fat catabolism.