Endocrine System and Hormones

Response to Stress

• Hormones responding to stress include cortisol, epinephrine, and norepinephrine.
• Generally, hormones responding to stress are hyperglycemic.

Types of Glands

• Endocrine glands secrete substances into the bloodstream and hormones to stimulate distant organs. They lack ducts.
• Exocrine glands secrete substances onto a surface through a duct.
• The pancreas functions as both an endocrine and exocrine gland, producing amylase (exocrine) and insulin (endocrine).

Endocrine System

• The endocrine system consists of ductless glands that produce hormones.
• Hormones are secreted directly into the bloodstream for use throughout the body.

Metabolism

• Hormones govern metabolism, such as T3 and T4 (growth hormones).

Homeostasis

• Homeostasis refers to a state of equilibrium.

Growth and Development

• Bone growth typically stops around age 22.

Endocrine Glands

• Endocrine glands secrete hormones directly into the bloodstream.
• They regulate bodily functions, maintain homeostasis, and control metabolism, growth, reproduction, and stress response.

Neuroendocrine System

• The nervous and endocrine systems intertwine closely to maintain homeostasis.
• This system integrates the nervous and endocrine systems to regulate body functions.
• Hypothalamic control is central, alongside reciprocal interactions between the nervous and endocrine systems, to maintain homeostasis and respond to stimuli.

Hormones

• Neurons release neurotransmitters and neuromodulators at synapses.
• Neurosecretory cells secrete substances directly into the bloodstream.
• Chemical signals are released with the purpose to control activity of body tissues.

Types of Hormones

• Amines
• Glycoproteins
• Steroids

Steroids

• Steroid hormones are lipids derived from cholesterol and usually bound to proteins.
• Examples include activated vitamin D3, aldosterone, androgens, cortisol, estrogen, progesterone, and testosterone.

Biogenic Amines

• Biogenic amines, which are also known as amino acid derivatives, are synthesized from tyrosine.
• Hydroxylation of phenylalanine generates catecholamines.
• The adrenal medulla is part of the sympathoadrenal axis.
• Tyrosine hydroxylase is an enzyme that converts tyrosine to 3,4-dihydroxyphenylalanine, the rate-limiting step for production of catecholamines.

Fatty Acid Derivatives

• Example fatty acid derivatives are leukotrienes, eicosanoids, thromboxane, and prostaglandin.

Polypeptides

• Polypeptides that don't fit into the other categories instead are, an example being prolactin, somatostatin, and arginine-vasopressin.

Hormone action

• Autocrine hormones act directly on the cells that secrete them.
• Paracrine hormones affect adjacent cells.
• Endocrine hormones are released into the bloodstream and act on distant target cells.

Functional Hormone Action

• Releasing hormones secreted by the hypothalamus stimulate secretion by the anterior pituitary.
• Inhibitory hormones suppress hormone secretion.
• Tropic hormones stimulate growth and activity of other endocrine glands.
• TSH stimulates the production of T3 and T4 which are very important for brain maturation.

LH

• Predominantly functions in the maturation of reproductive organs.

Classes of Effector Hormones

• Effector hormones secreted by endocrine glands target other non-endocrine tissues.
• Each hormone has unique tissue actions.
• An example is Prolactin a lactogenic hormone to the mammary glands that facilitates the production of breast milk.

All Glycoprotein Hormones

• All the following hormones except Growth Hormone are glycoproteins
• Thyroid Stimulating Hormone
• Follicle Stimulating Hormone
• Luteinizing Hormone

All Amine Hormones

• All the following hormones except Tetraiodothyronine are amines
• Epinephrine
• T3 and rT3
• Thromboxane

Hypothalamus

• The hypothalamus regulates various bodily functions via control over the endocrine system and autonomic nervous system.
• It mediates between the nervous and endocrine systems.
• Also, responsible for the production of releasing hormones.

Primary Function of Hypothalamus

• Functions for homeostasis and contributes to change in the body's fluid.
• If there is change in sodium levels, the hypothalamus will respond right away.

Osmolality

• Increase or decrease to sodium concentration is clinically significant.
• Sodium is a major contributor to osmolality in the bloodstream.

ADH

• Arginine vasopressin travels to the nephrons to reabsorb water. ADH stimulates distal convoluted tubules.
• A sodium level of 135-145 mmol/L is sufficient for kidneys to excrete water. A stimulus to use ADT.

Pituitary regulation

• The pituitary gland makes the hypothalamus responsible for homeostasis.
• However, the the pituitary responds to the hypothalamus to stimulate other endocrine glands.
• The hypothalamus releases TRH which causes the pituitary to produce TSH which is related to the thyroid. The pituitary glad cannot detect and and function in a feedback loop on it's own.

The Hypothalamic-Pituitary-Thyroid Axis

• Chain of Command for the Endocrine system:
• Pituitary gland releases hormones to the bloodstream.
• Hypothalamus releases TRH, then the pituitary gland releases TSH to the organ tissues, The thyroid produces and releases T3 and T4.

Hormones

• Growth Hormone Releasing Hormone (GHRH): Releases growth hormone.
• Gonadotropin-Releasing Hormone (GnRH): Releases LH and TSH.
• Corticotropin-Releasing Hormone (CRH): Releases ACTH.
• Thyrotropin-Releasing Hormone (TRH): Releases TSH.
• Prolactin-Releasing Hormone (PRH): Stimulates Prolactin.

Feedback Mechanisms

• Feedback mechanisms regulate hormone secretion by turning it on and off.
• They also occur because stimuli inform our bodies that an action needs to be performed.

Types of Feedback

• Negative Feedback Loop: "Controlled Defiance"
• Positive Feedback Loop: "Controlled Amplification"

Example of Feedback

• If there's a decrease in T3 and T4, the production of TRH increases (negative feedback).
• Hypothalamus amplifies the signal through the production of TSH (positive feedback). The production of T3 and T4 are activated so therefore the TRH slows down.

Releasing Hormones

• Most releasing hormones stimulate the adenohypophysis.
• Different cell types exist in the adenohypophysis which gives a single gland ability to multiple production.

GHRH

• If the hypothalamus causes production of GHRH then cells in the anterior pituitary that respond to the hormone are the cell type Somatotrophs.
• Stimulating using Corticotrophs, stimulate CRH, and the cells that respond form Corticotrophs.

Cause-and-effect

• Endocrine glands are cause-and-effect as is their stimulating factors GHRH with Gonadotrophs.

Hierarchy of Commands

• Pituitary gland is the "boss" since the pituitary has direct links to hormones. However, the hypothalamus is ultimately in charge and controls the pituitary.

Production Control

• If there's an overstimulation of hormones being produced, glands will act as an inhibitor to maintain all commands.

Feedback Loop

• For the endocrine glands, if one gland is positive, the gland after returns negative.
• Most of the time for endocrine glands, putting both hormone systems in the picture always comes down to + --> - --> + --> - etc and vice versa

Pregnancy

• Amplifies the process if there are uterine contractions, it is detected by the hypothalamus. It will produce more oxytocin.
• One can refer to pregnancy as a positive feedback mechanism.

Which Two Types

• Oxytocin (posterior pituitary) and Arginine Vasopressin (AVP) are synthesized in the hypothalamus.

Not Correct

• A TSH relationship (TSH: T3 and T4) is not associated. Adrenocorticotropic hormone ACTH: is in relationship with Aldosterone.

Tropic Or Not

• ACTH and TSH are tropic hormones, while GH and prolactin are direct effectors.

Master Gland

• The Pituitary Gland is an important component since all hormones stimulate other parts of the body.
• Other areas cannot fully function without a command from the pituitary; if an outlier, there will be indication of tumor.

Key concepts as the pituitary gland

• A master gland, separated into a main one, anterior, along with an intermediate, and posterior side with an anterior of the pituitary gland.

Anterior Lobe Cell Three types

• Chromophobes, acidophilic, and basophilic, all types capable of hormone production. These main points important for hormone and protein.

Growth hormones

• Growth hormones produced in adenohypophysis (anterior pituitary), acting as a single peptide. Structurally linked with human placenta,
• There are various stimulus like the somatomedin that is very active and affected along various direct and trophic areas.

Glycoprotein Hormes

• GHRH, GH (multiple) will be released with the use of these components. FSH is inhibin and LH will effect the sexsteroids.

Anterior

• Anterior of the pituitary (key), affecting tropic and stimuating somtatropin with sleep, exercise, and proper somamendrin.

Hormone in all areas

• An increase in TSH as the process of the Follics increase and are tested, producing the main cells in the thyroid.
• The thyroid is critical in governing metabolism and other bodily functions.

3 thyroid hormones

• T3
• T4
• rT3

7 functional areas

• In the areas of each main point, from 3 glands to the medulla, there are functions and capsule production for hormones. Such hormone activity will test for 1 - 5 picometers

Negative Feedback

• To maintain T3 levels, there must also be lower concentration such as the range of a negative number or a bit before.
• Also for the use of various electrolyte components to help produce this factor.

3 types of thyroid related releases for hormone production.

• For hyperthyroidism, the endocrine portion becomes an issue, with T3 and T4 overproduced.
• For primary disorders, they become an issue with the main endocrine, where hormones such as T3 and T4 are elevated.
• Secondary types are issues with the pituitary.

Primary versus secondary

• Primary - The thyroid is the problem source, either tumor or the thyroids stimulating the hormone.
• Secondary - A tumor is the is the reason to the hormone problem

Test on what is working effectively

• The test performed is what components working is not directly for each cell. Thyroid stimulating hormone test is still required.

How to help

• For the use of some 3D types, the thyroid can be tested using the enzyme in each to make test more effective since are just not immediately used.

Thyroid production

• Has direct relations with the function and control that is with each organ with each function. There need is a feedback component.