Physiology Exam 3 (Modules 11-15)

Endocrine, Immune, Excretory, Digestive, Reproductive system, and deriving energy

Anatomy of the Pituitary Gland

Anterior Lobe:

• Produces and secretes the hormones of pituitary

• Regulated by hypothalamus through hypophyseal portal system (via hormones secreted by hypothalamus)

Posterior lobe:

• Stores and secretes hormones

• Hypothalamic nerves regulate it

Generic Hormone Axis

Hypothalamus → Neuroendocrine hormones (receive signals from the nervous system and respond by secreting hormones into the blood stream) → Pituitary Glands → Tropic Hormone (regulate the activity of other endocrine glands) → Target Organ → Systemic Hormone

Negative feedback loop

Anterior vs Posterior Hormones

Anterior:

• Growth Hormones (Bones, muscles, and organs)

• Prolactin (milk production)

• Ovaries (Estrogen and Progesterone)

• Testes (Testosterone)

• Adrenal Cortex (Cortical hormones)

• Thyroid Gland ( Thyroid hormones)

Posterior

• Oxytocin (releasing milk)

• Uterus

• Kidneys

Hypothalamic- Pituitary Growth Axis (HPS)

Non-uniform regulation (growth spurts)

GHRH (Growth hormone- releasing hormone) regulates growth hormones

Somatostatin (Growth Hormone- Inhibiting Hormone (GHIH))

Ghrelin (hunger hormone)

Diurnal Rhythm (process that cycles every 24 hours) (external factors like light drive it)

Growth Axis

Hypothalamus → Anterior Pituitary → GH

Factors such as:

• Genetics

• Environmental/ internal influences:

-Exercise (+)

-Stress (-)

-Nutritive Status (Amino acids +) (Fatty acids -)

-Sleep (+)

GH activity

Bind directly to receptors (liver, fat, muscles)

• fatty acid in blood, decrease glucose uptake

- Muscles run on fat

-More glucose for the brain

• INDIRECTLY stimulates amino acid uptake and protein synthesis vis Insulin-like growth factors (IGFs)

Insulin like Growth Factors (IGF)

1.) 2 extracellular messengers bind to 2 receptors, which activates receptor’s protein kinase site

2.) Protein Kinase site self- phosphorylates receptor’s tyrosines

3.) Inactive designated protein binds to receptor, which phosphorylates the protein, activating it

IGFs causes

hyperplasia (cell division)

hypertrophy (cell enlargement)

Prolongs cell life span

Increases synthesis of DNA, RNA, and proteins

IGF-I

Released by the liver in response to GH

IGF-II

Doesn’t respond to GH

Involved in fetal growth

GH-Negative Feedback

IGF-I affects Somatostatin and GHRH via the hypothalamus and GH secretion

Negative for GH and positive for Somatostatin

Pituitary Dwarfism

Short stature with normal proportions @ birth and can develop

Gigantism

Excessive growth in children (before puberty)

Acromegaly

Excessive GH after puberty

Hypothalamic- Pituitary Thyroid Axis

Thyrotropin-releasing hormone

Thyroid stimulating hormone

Production of Thyroxine (T4) and tri-iodothyronine (T3)

T4+ T3 = Thyroid hormone

Bind to plasma proteins

Consistent secretion

Thyroid Hormone Activity

-Initiates transcription of specific mRNAs

-Increases overall metabolic rate by influencing mitochondrial activity and Na+/K+ pumps

-Low Levels → fuel storage

-High Levels → fuel catabolism (break down of molecules)

Developmental effects

-Vertebrate CNS

-Life history s