Anatomy Lesson 22-Intro to Endocrine and the Pituitary Gland

Endocrine vs Nervous System

Nervous System: Direct connection to target cell (the nerve to move your hand muscles needs to be close to your hand). Work within millseconds and effects are brief.

Endocrine System: Hormone enters the blood to circulate throughout the body and affect the activity of a distant cell (the hormone producer to control uterine contractions doesn’t need to be near the uterus). Can take seconds, hours or even days to start working and kick in.

Some chemicals function as neurotransmitters and hormones (norepi)

Exocrine vs Endocrine Glands

Exocrine: Secrete products into ducts (sweat glands, digestive glands, etc:)

Endocrine: Secrete products into the blood or tissue fluids (parathyroid)

Atypical Endocrine Gland (2 examples)

An atypical endocrine gland performs endocrine functions but is not classified like a typical endocrine gland. This is because these tissues have other primary functions but releasing hormones is their side hustle.

Example 1; Adipocytes: Make leptin when they are full of energy. Leptin binds to receptors in the hypothalamus to signal satiety (fullness).

Example 2; Stomach: The stomach releases ghrelin when it’s empty. Ghrelin binds to receptors in the hypothalamus to signal hunger.

2 types of hormones (and 2 subtypes)

Circulating Hormones: travel through the blood to distant tissues

Local Hormones: Work closer to home

• Paracrine: Act on nearby cells

• Autocrine: A hormone that works on the same cell that released it

Lipid Soluble Hormones and it’s Course of Action

• Do not dissolve in water

• Circulate through the blood by riding on carrier protiens

• Cross the plasma membrane and act on intracellular receptors that affect gene transcription

Course of Action

• Lipophyllic hormone diffuses through the plasma membrane into the cell and binds to a receptor

• The receptor hormone complex binds to response elements on DNA (promoter or enhancer region) to alter gene expression

• Newly formed mRNA instructs ribosomes to create specific protiens

• New protiens alter cellular activity

Water Soluble Hormones and their Course of Action

• Dissolve in water and travel by themselves in blood

• Cannot cross the plasma membrane, so receptors on top of the plasma membrane recieve them which generates second messengers in the cytosol

Course of Action

• Hydrophyllic hormone binds to receptor on plasma membrane and activates a G-Protien

• The G-Protien activates adenylate cyclase which converts ATP to cyclic AMP (cAMP).

• cAMP activates protien kinases

• Activated protien kinases phosphorylate cellular protiens

• When millions of cellular protiens get phosphorylated it causes reactions that produce physiological responses

How does Epinepherine Act on Smooth Airway Muscles? What type of hormone is this?

Hydrophyllic Hormone

1) Epinephirine (1st messenger) binds to Beta 2 receptor on the plasma membrane

2) This activates a G-Protien which activates adenylate cyclase

3) Adenyate Cyclase converts ATP to cAMP (2nd messenger)

4) cAMP activates protien kinase A (PKA)

5) Lots of PKA results in relaxation of smooth muscles as contractions are stopped

How does Oxytocin Affect Uterine Contractions and the Myoepithelial Cells of Lactiferous Ducts

1) Oxytocin binds to the cell receptor on the plasma membrane

2) This activates a Gq Protien which activates phospholipase C.

3) Phospholipase C converts PIP2 to IP3 and DAG (2nd messengers)

4) IP3 signals for release of calcium from the SR while DAG signals for calcium channels in the cell to open and let calcium in.

5) Calcium causes muscle contraction

3 main ways to regulate hormone secretion

• Most endocrine hormones are released in short bursts. Stimulation leads to more frequent bursts

• Regulation of secretion ensures that over or underproduction doesn’t occur

• MOSTLY negative feedback

1) Signals from the Nervous System

2) Chemical Changes in the Blood

3) Other Hormones

Anterior Pituatary

-Outgrowth of ectoderm of the roof of the mouth’

-Adenohypophysis (more of a gland)

Posterior Pituatary

-Outgrowth of the ectoderm of the base of the hypothalamus'

-Neurohypophysis

Relational Anatomy of the Pituatary and it’s application

-The pituatary and sphenoid sinus are seperated by a paper thin section of bone. This makes surgeries like transphenodal hypophysectomy easier as the pituatary can be accessed via that sinus

-The optic chiasm is also anterior and superior to the pituatary. This means that pituatary tumors (mainly occuring on the adenohypophysis) can damage the optic chiasm and lead to diplopia

Blood Supply of The Pituatary

-The anterior and posterior pituatary have nothing to do with one another

-They have seperate blood supplies (arise from internal carotid)

-The anterior pituatary is supplied by a portal system which has very low pressure. Damage to this system, such as a hemorraghe can lead to the pituatary not working (panhypopituatarism)

-Anterior Pituatary: Superior hypophyseal artery»Capillary bed»Hypophyseal portal viens»capillary bed»Anterior hypophyseal viens

Hormones of the posterior pituatary (2)

ADH/Vasopressin

-Large doses cause vasoconstriction

-Makes you not pee

-Release is stimulated by increased blood osmolarity, low BP or pain. It is inhibited by alcohol

Oxytocin
-Stimulated by stretch of cervix or nipple stimulation

-Uterine contractions or breast milk

Hormones of the anterior pituatary (6)

TSH

-Released in response to thyrotropin releasing hormone

-Causes thyroid to start working

Follicle Stimulating Hormone

-Released in response to gonadotropin releasing hormone

-Stimulates production of gametes

Leutinizing Hormone

-Released in response to GnRH

-Stimulates production of sex steroids

Adrenocorticotropic Hormone

-Released in response to corticotropin releasing hormone

-Stimulates production of hormones in adrenal cortex

Growth Hormone

-Released in response to growth hormone releasing hormone

-Causes growth of bones, muscles and other tissues

Prolactin

-Released in response to prolactin releasing hormone

-Stimulates milk production in the breast

Regulation of Growth Hormone Release

Hypoglycemia releases GHRH to help the body break down fat and create glucose. Hyperglyceima releases GHIH to inhibit glucose production.

-Before the epiphyseal growth plate closes, GH works on that area to make more bone

-After the epiphyseal growth plate closes GH only works on the hands feet and face

Gigantism

GH levels rise before epiphyseal growth plate closes. Super tall

Acromegaly

GH levels rise after growth plate closes. Growth in face, hands and skin.

Prolactin Regulation

-Regulated by prolactin releasing and prolactin inhibiting (dopamine) hormone.

-Prolactin releasing hormone is released during early menstruation and pregnancy (more prolactin)

-Prolactin inhibiting hormone is inhibited just before menstruation and by infant suckling (meaning you have less stuff inhibiting prolactin release)

-Mammary glands must first be primed by other hormones like estrogen and progestoerone for prolactin to have milk producing effects

-Too much prolactin can cause galactorrhea (unnecesary milk production outside of pregnancy), ammenorrhea and impotence

-Too little prolactin can cause lack of milk production, infertility/subfertility