Physiology Block 2

Endocrine system goals

The coordinate and integrate cellular activity and to maintain homeostasis

The endocrine system facilitates communication across ______ within the body

organs

Homeostasis is often an interplay between the brain and body via what actions?

Hormone

Examples of exocrine gland functions

Sweating and breastfeeding

Exocrine glands are associated with secretions going ________ the body

outside

Endocrine glands are associated with secretions going ________ the body

inside

What are the three major chemical classes of hormones?

Amines, peptides & proteins, and steroids

Amines key features

Derived from amino acids

Peptides and proteins key features

peptides = short proteins

Steroids key features

hydrophobic and lipophilic

Norepinephrine, Epinephrine, and Dopamine are apart of what hormone group?

Catecholamines

T3 and T4 are what hormones?

Thyroid (tetra/tri iodothyronine)

How do endocrine glands send signals?

Through the bloodstream

What are amine hormones derived from?

The Amino Acid Tyrosine

Chemicals can be both ________ and ___________

hormones, neurotransmitters

Multiple Tyrosines make up what hormones?

Thyroid

Insulin is what kind of hormone?

Peptide

Peptide hormones are stored in

vesicles

Prepro and pro are two prefixes that determine that a hormone is what?

Inactive

What is the key building block of steroid hormones?

Cholesterol

What determining factor of steroid hormones makes it to where they cannot readily dissolve in aqueous solutions?

4-ring structure

What are the 4 main classes of steroid hormones?

Cortisol, aldosterone, testosterone, and estradiol

Cholesterol serves what two main functions?

Helps support cell membrane structure and is a precursor to steroid hormones

Hormones must to what in order to take action?

Bind to their receptors

In autocrine signaling, where is the receptor located?

On the endocrine cell itself

In paracrine signaling, where is the receptor located?

On a distant target cell

Lipophilic and hydrophobic hormones tend to be transported through the blood via what?

Binding proteins

Free, active hormones continue to signal until what?

Metabolized to an inactive form

What is half-life?

The time it takes to clear half of the hormone from circulation

What is the major organ of hormone metabolism (making hormones inactive)?

Liver

Cell surface receptors facilitate what?

Signals from outside the cell to inside the cell

Intracellular receptors

Often deep in the nucleus of the cell, binding functions to turn DNA/gene transcription on

The ability of a cell to respond to a hormone depends on what?

The presence of receptors for that hormone on or in the target cell

What is up-regulation?

An increase in the number of receptors for a hormone

What is down-regulation?

A decrease in the number of receptors for a hormone

Inputs that control hormone secretion

Ions or nutrients, neurotransmitters, and hormones

What is the master regulator of the brain and body?

Hypothalamus

What does the hypothalamus regulate?

Central Brain Circuitry (motivation) and Pituitary/Systemic (hormonal)

Where is the hypothalamus located?

At the base of the brain

What is the posterior pituitary referred to as?

An extension of the brain

What is the anterior pituitary referred to as?

True glandular tissue/true endocrine cells

How does the posterior pituitary gland function?

Hormones are made and are trafficked down the axons and eventually released into the bloodstream

How does the anterior pituitary gland function?

Axons that terminate halfway down the pituitary gland and turn into the median eminence. Hormone one is released at the median eminence and initiates the endocrine cells that release hormone two into the bloodstream.

What kind of target cells release “hormone two” into the blood stream in the anterior pituitary gland of the hypothalamus?

Pituitary target cells, or “-trophs”

What two hormones are released from the posterior pituitary?

Oxytocin and vasopressin

Luteinizing hormones and follicle-stimulating hormones are secreted through ____________ that are scattered throughout the anterior pituitary

gonadotrophs

CRH hypothalamic factor impedes on what anterior pituitary cells and produces what pituitary hormone?

Corticotrophs, includes ACTH and B-endorphin

TRH hypothalamic factor impedes on what anterior pituitary cells and produces what pituitary hormone?

Thyrotrophs, Thyroid-Stimulating Hormone (TSH)

GnRH hypothalamic factor impedes on what anterior pituitary cells and produces what pituitary hormone?

Gonadotrophs, LH and FSH

GHRH hypothalamic factor impedes on what anterior pituitary cells and produces what pituitary hormone?

Somatotrophs, growth hormone

Dopamine hypothalamic factor impedes on what anterior pituitary cells and produces what pituitary hormone?

Lactotrophs, prolactin (normally turned off)

The hypothalamus uses what to maintain homeostasis and terminate the release of hormones?

Negative feedback

What hormones are made in the hypothalamus and released in the posterior pituitary?

Oxytocin and Vasopressin

Key aspects of Oxytocin

Target organ is the uterus and mammary myoepithelial cells, causes uterine contraction and milk ejection

Key aspects of Vasopressin

V1 receptors are associated with smooth muscle cells and cause vasoconstriction

V2 receptors are associated with kidney collecting ducts and cause increased water retention

Oxytocin increases cellular ______ levels

calcium

Myosin Light Chain Kinase serves as a bridge between…

increased calcium levels and muscle contraction

Kinase

A specialized protein or enzyme that attaches a phosphate group from an unactive protein to make it an active protein

Myosin

a muscle protein responsible for muscle contraction

Why does smooth muscle contraction require oxytocin?

Oxytocin increases the intracellular calcium levels, allowing calcium to bind to calmodulin and make the Myosin Light Chain Kinase function

Baroreceptor reflex process in response to low BP

Low BP leads to decreased baroreceptor stimulation in vasculature, hypothalamus is stimulated, increased vasopressin release into bloodstream, increased vasoconstriction via smooth muscle contraction, increased blood pressure, homeostasis restored

Osmoreceptor response process to dehydration

Dehydration leads to increase Na+ concentration in ECF, osmoreceptors are stimulator, increases vasopressin release and thirst, leads to decreased urinary water loss and increased water gain, additional water dilutes ECF and volume increased

Vasopressin increases the levels of __________ in kidneys to retain water

aquaporins

What are the coordinated effects of Vasopressin?

Increased Blood Pressure and Volume

What is the Hypothalamic-Pituitary-Thyroid (HPT) Axis?

A series of events where hormones are released from the hypothalamus that act on the anterior pituitary, where hormones are released from the anterior pituitary that act on the thyroid gland, where hormones are released from the thyroid gland that travel through the bloodstream and enact negative feedback on the hypothalamus and anterior pituitary

Homeostasis is mediated by what?

Feed-forward and negative feedback loops

Where is the thyroid located?

At the front of the throat

Why is iodine a necessary nutrient?

Stimulates the production of thyroid hormones

What is the purpose of the Thyroid Stimulating Hormone (TSH)?

Binds the TSH receptor on the thyroid gland and stimulates the release of hormones T3 and T4 from the thyroid gland

The thyroid gland is made up of numerous ________

follicles

The ______ is a protein-rich center where thyroid hormone is synthesized and stored

colloid

Since human diets don’t contain a lot of iodine, what serves as a store of iodine in the body?

The colloid of the thyroid gland

Follicular epithelial cells

Surround the colloid and participate in almost all phases of thyroid hormone synthesis and secretion

Thyroglobulin

A protein enriched in the Thyroid gland (present in high levels). Source of Tyrosines for Thyroid Hormone. Made up of a bunch of Tyrosine amino acids

What two molecules do you need to create Thyroid hormones?

Iodine and Tyrosine

Thyroglobulin acts as a ______ for Thyroid Hormone Synthesis

scaffold

What determines T3 from T4 at the structural level?

The amount of Iodine bound to the hormone

What determines T3 from T4 at the functional level?

T3 is the active form, T4 is the inactive form. T4 can be converted into T3 which is why it is still synthesized even though inactive.

What is an absorptive state?

Fuel uptake (eating)

What is a postabsorptive state?

Fuel utilization (running)

Absorptive states are associated with what phase?

Anabolic

In an absorptive state, what happens in terms of units?

Building of larger units from smaller units (anabolic)

Postabsorptive states are associated with what phase?

Catabolic

In a postabsorptive state, what happens in terms of units?

Breakdown of larger units into smaller units (catabolic)

What happens in an anabolic reaction?

Small molecules and energy are used to create large molecules

What happens in a catabolic reaction?

Large molecules are broken down into smaller molecules and energy

Glycogen is a storage version of what?

Glucose

What is the main function of the pancreas?

Regulating blood-glucose levels

What contains both exocrine and endocrine producing tissue?

Pancreas

What is the major energy source of cells during an absorptive state?

Glucose

What are the major energy source of cells during post-absorptive states?

Fatty acids and ketones

Glucose storage by the liver occurs during what state?

Absorptive

Glucose release by the liver and gluconeogenesis occurs during what states?

Post-absorptive

What two secretions does the pancreas produce?

Hormones and enzymes

What does an organ being heterocrine mean?

Contains both exocrine and endocrine tissues

How much of a role (in percentage) does the pancreas play with endocrine hormone production?

1%

Iodide is cotransported with what molecule?

Na+

What enzyme allows Iodine to bind to Tyrosine?

Thyroid Peroxidase

Thyroid peroxidase (TPO) is exclusively located in what structure?

Thyroid colloid

Presence of TPO in the blood indicates what?

Autoimmune destruction of the thyroid