Endocrine System Flashcards
Endocrine System function
Helps establish Homeostasis
Homeostasis : sense of balance even when there are changes in the external environment. (Internal conditions maintained by living things)
Types of Hormones
Steroids
Non-steroids
Steroid Hormones
Made from cholesterol by adrenal glands as well as the gonads.
They are hydrophobic (non-polar), so they travel through the bloodstream bound to TRANSPORTED PROTEINS to reach their target cells.
Because they are relatively small and non-polar, they are able to diffuse right across the phospholipid membrane of target cells and bind to an intracellular receptor.
Non-steroid Hormones
Are either peptides or proteins (so chains of aa’s) or they can derived from a single aa.
They never enter the cell.
- Peptidic Hormones: like Insulin and Glucagon are Hydrophilic. They cannot pass through the phospholipid bilayer. They bind a cell SURFACE RECEPTOR PROTEIN.
- Amino Acid Hormones: Derived from the aa Tyrosine (Tyr).
- Thyroid hormones
- Adrenaline (Epinephrine)
- Noradrenaline (Norepinephrine)
–> This hormones are synthesized differently, the tweaks here and there make them behave differently. either more like steroids or peptides.
Thyroid Hormones
Behave more like steroid hormones. They travel the bloodstream bound to a TRANSPORTED PROTEINS and cross the membrane to bind to a intracellular receptor.
Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine)
Behave more like peptide hormones. Travel through the blood unbound and bind to a cell SURFACE RECEPTOR PROTEIN which set up intracellular changes.
Partly responsible for the increase of blood flow to the heart and the muscles that happens in a “fight or flight response”.
Endocrine Glands.
- Hypothalamus: The CEO - Gives the order
- Pituitary gland: 1st officer - Enforces it (the order)
( this two work closely to make hormones that help control the production of other endocrine glands) - Thyroid
- Adrenal glands
- Gonads
Pituitary gland
Made of two lobes:
- Anterior lobe - glandular tissue
- Posterior lobe - axons coming from the hypothalamus
Hypothalamus
Is the link between the nervous and the endocrine system. because it has neural functions and endocrine functions is called an neuroendocrine organ
Receives information from the entire body regarding all sorts of things - body temp, blood osmolarity, danger - and responds by producing hormones that are stored in the posterior pituitary to be released later. OR hormones that act on the anterior pituitary making it secrete some hormones of its own.
Hypothalamus and Anterior Pituitary: Hypothalamic Hormones - Stimulatory
Stimulatory (releasing hormones)
- Thyrotropin (TRH)
- Corticotropin (CRH)
- Gonadotropin (GnRH)
- Growth Hormone (GHRH)
These make the anterior pituitary synthesize its own hormones in response. (Hypothalamus -> A. Pituitary-> gland). They have a negative feedback loop, when the hormone increase it sends a signal to the hypothalamus to stop
- TRH –> Thyroid stimulating hormone (TSH) –> Thyroid –> Thyroid hormones
- CRH –> Adrenocorticotropic hormone (ACTH) –> Adrenal Gland –> Cortisol
- GnRH –> Gonadotropins (FSH, LH) –> gonads –> production and maturation of gametes and production of sex hormones. (exception to negative feedback on ovulation - positive feedback)
- GHRH –> growth hormone (GH) –> effect on long bones & other tissues making them grow.
Hypothalamus and Anterior Pituitary: Hypothalamic Hormones - Inhibitory.
Inhibitory Hypothalamic Hormones
* Growth hormone inhibiting hormone (GHIH or Somatostatin). Also synthesized by the digestive tract which tells the hypothalamus to lessen the GH production.
- Prolactin Inhibiting factor (Dopamine). Prolactin only needed in milk production, so the hypothalamus continuously secretes Prolactin Inhibiting factor which goes to the anterior pituitary and inhibits prolactin.
Hypothalamus and Posterior Pituitary
Connected by the pituitary stalk made up of the axons of hypothalamic neurons coming specifically form the PARAVENTRICULAR AND SUPRAOPTIC NUCLEI.
Both of this Nuclei secrete.
* Antidiuretic hormone (ADH or Vasopressin)
* Oxytocin.
In the posterior pit. there are Herring Bodies, which store hormones until they receive a signal to release them.
When time is right the axons release ADH or Oxytocin into the p.p capillaries and from there into the systemic circulation.
Singal for release of Antidiuretic hormone (ADH or Vasopressin) and what does it do.
High blood osmolarity or a low blood volume.
* ADH helps retain water form the urine & causes vasoconstriction of the blood vessels –> helps decrease blood osmolarity and increase pressure
Singal for release of Oxytocin and what does it do.
Childbirth
- Dilates cervix and stimulates uterine contractions during childbirth.
- Contracts muscle cells in breastfeeding to ject the milk.
- Aside from motherhood Oxytocin levels are generally low.
- They increase a bit during pleasant interactions (hug, physical contact, orgasm)
Pineal Gland: name of cells and what releases
Composed of cells called Pinealocytes – Synthesize and release Melatonin.
Melatonin is mostly secreted in the night and regulates our body’s Circadian Rhythm (tell us when we should be sleeping and we should be awake)
Thyroid gland
Made of a right and left lobe, made of thousands of follicles that makes:
- Triiodothyronine (T3)
- Thyroxine (T4)
Once inside the cell T4 is mostly converted to T3 –> T3 speeds up the basal metabolic rate.
In Between the Thyroid follicles there are parafollicular cells (C-Cells) which secrete a hormone called Calcitonin.
In the back of the Thyroid gland there are Parathyroid glands (four in total), they make Parathyroid hormone
Calcitonin & Parathyroid hormone: Involved in Calcium, Phosphate and bone Metabolism. Regulated by calcium levels in the blood.
Adrenal Glands
Above each kidney.
Each is made of an outer layer called the Cortex surrounding a core called the Medulla.
Cortex (divided in 3 zones that produce Steroid H. )
- Zona Glomerulosa - Aldosterone
- Zona Fasciculata - Cortisol
- Zona Reticularis - small amount of sex hormone precursors
Aldosterone is secreted when and what does t do:
When there is low blood pressure, or when there is too much potassium in the blood.
Upon release:
- Prevents water and sodium loss in the urine.
- Increases the elimination of potassium
Cortisol is secreted when and what does t do:
Known as the stress hormone.
Secreted during fight or flight situations, along with Adrenaline & Noradrenaline (which are secreted near by in the adrenal medulla)
Pancreas
Exocrine part- Helps with digestion.
Endocrine part - secretes Insulin and Glucagon.
Exocrine part- secretes digestive enzymes directly to the Duodenum, which helps break down food into nutrients the small intestine can absorb.
Endocrine part - is made up of Beta cells and Alpha cells:
- Alpha cells - In low blood sugar- release Glucagon – binds to a receptor in the liver cells that respond by activating enzymes that break down glycogen and release glucose in the bloodstream. (liver has stored glycogen)
- Beta cells - in High blood sugar - release Insulin into blood to help cells uptake glucose and use it for energy - lows blood sugar (after meals)
