Endocrine Flashcards
Compare and contrast the general control of body functions by the nervous and endocrine systems.
Nervous system:
- Regulates the activity of muscles and glands
- Regulates via electrochemical impulses delivered by neurons and neurotransmitters
- Organs respond within milliseconds (aka reacts quickly to stimuli)
Endocrine system:
- Influences metabolic activity by means of hormones
- Hormones are secreted by cells into the extracellular fluid, travel through the blood, and regulate the metabolic function of other cells in the body
- Hormones control and integrate processes like reproduction, growth and development, maintenance of electrolyte, water, and nutrient balance of the blood, regulation of cellular metabolism and energy balance, mobilization of body defenses
- Regulates processes that go on for relatively long periods of time
Distinguish between endocrine and exocrine glands.
Endocrine glands: aka ductless glands, produce hormones and release them into the surrounding tissue fluid, typically having a vascular and lymphatic drainage that receives the hormones and leads hormone to a target cell
Exocrine glands: produce nonhormonal substances (e.g. sweat, saliva), and have ducts that carry these substances to a membrane surface
What is a hormone? a target cell?
Hormone: chemical messengers secreted by cells into the ECF, then they travel through the blood to target cells, alter target cell activity and decreasing or increasing rates of normal cellular processes
Target cells: cells which have a receptor specifically able to recognize and bind to a particular hormone molecule
What enables certain cells to respond to a hormone, while others cannot?
The receptors on the cell must be specific to the hormone
Distinguish between classical endocrine signaling, paracrine signaling, and autocrine signaling.
Endocrine signaling: chemical is secreted blood circulates through the blood and diffuses to other areas of the body, more long distance than paracrine and autocrine signaling; diffuses through the blood to get to target cell
Paracrine signaling: chemicals act locally (within the same tissue) but affect cell types other than those releasing the paracrine chemicals; paracrine cells release a secretion that diffuses through the ECF to a target cell in the local area (does not go through the blood, just ECF)
Autocrine signaling: chemicals that exert their effects on the same cells that secrete them
In terms of their general chemistry, hormones can be broadly classified as amines, peptide or protein hormones, and steroid hormones. Explain the basic difference between each of these classes and list several examples of each class of hormone.
Amino acid based hormones include amines, peptide, and protein hormones. They are usually water soluble and cannot cross the plasma membrane.
Amine hormones: hormones that are simple amino acid derivatives; e.g. epinephrine, thyroxine
Peptide hormones: hormones that are made up of short amino acid chains; e.g. prolactin, oxytocin, insulin
Protein hormones: hormones that are made up of long polymers of amino acids; e.g. growth hormone
Steroid hormones: a category separate from amino acid based hormones. Steroid hormones are synthesized from cholesterol. They are all lipid soluble and can cross the plasma membrane; e.g. gonadal and adrenocortical hormones
Which class of chemical messenger is derived from cholesterol? from amino acids? from arachidonic acid?
Derived from cholesterol: steroid hormones
Derived from amino acids: amine hormones, peptide hormones, protein hormones
Derived from arachidonic acid: eicosanoids
Hormones in the biogenic amine class are all derived from a single amino acid. From what amino acid are the catecholamines (i.e., epinephrine and norepinephrine) and thyroid hormones derived? From what amino acid are serotonin and melatonin derived?
Catecholamines and thyroid hormones: tyrosine
Serotonin and melatonin: tryptophan (melatonin is derived from serotonin)
Name the individual steroid hormones presented in this chapter. Identify the site of secretion for each of the steroid hormones.
Gonadal hormones - ovaries and testes
Adrenocortical hormones - adrenal glands
Arachadonic acid is a fatty acid present in phospholipid membranes (e.g., the plasma membranes of cells). It can be cleaved from plasma membranes and metabolized via 2 main enzymatic pathways, resulting in a class of chemical messengers called \_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Eicosanoids
What are the main subtypes of eicosanoids? Why are these chemical messengers not considered to be true hormones?
The main subtypes are leukotrienes and prostaglandins
The effects of eicosanoids are typically highly localized, affecting only nearby cells, they generally act as paracrines and autocrines and do not fit the definition of true hormones
Which hormones affect their target cells by binding to an intracellular receptor?
Lipid-soluble hormones (steroid and thyroid hormones* (*lipid-soluble but also amino acid based))
What is the general mechanism through which the hormones identified above (#12) induce changes in their target cell’s metabolism.
Direct gene activation
Describe the specific steps in direct gene activation by a lipid-soluble hormone (note that thyroid hormone also exerts its effect via direct gene activation).
- Steroid hormone diffuses through the plasma membrane and binds to an intracellular receptor, activating the receptor and becoming a hormone-receptor complex
- H-R complex enters the nucleus and makes its way to the nuclear chromatin
- H-R complex binds to portion of DNA region specific to the H-R complex
- Binding initiates transcription/alters the rate of transcription of the specific gene to mRNA
- The mRNA directs protein synthesis
Where are the receptors for amine and peptide hormones located?
In the plasma membrane of the target cell
Describe the process of G protein activation (in your explanation include the role of the
hormone, its receptor, GDP, GTP, the alpha subunit and the dimmer).
For water-soluable hormones
- Hormone (this is the first messenger) binds to its receptor in the plasma membrane
- Hormone binding causes the receptor the change shape, which allows it to bind a nearby inactive G protein (G proteins are heterotrimeric in structure (3 different subunits - alpha, beta, and gamma)). The G protein is activated as the GDP bound to its alpha subunit is displaced and replaced by GTP (higher energy than GDP)
- GDP being replaced by GTP activates the G protein and causes the alpha subunit to dissociate from the beta-gamma dimer.
Describe the specific steps in the activation of the cAMP second messenger system.
Continuation of signal transduction from question 16
- The dissociated alpha-GTP moves along the membrane and binds to adenylate cyclase (an effector enzyme).
- Adenylate cyclase generates cAMP from ATP
- cAMP activates protein kinase A (enzymes that add phosphate group to proteins aka phosphorylates proteins), protein kinase A produces a cascading amplifying physiologic effect (changes cell activity)
Why is cAMP called a “second messenger”?
Because cAMP triggers a transduction cascade once activated
What is the function of phosphodiesterase (PDE)? How is PDE activated?
Phosphodiesterase (PDE) degrades cAMPs, therefore stopping signal transduction
PDE is activated by protein kinase A
Explain why second messenger systems are said to have an “amplifying effect” on the
initial hormone signal.
Each activated adenylate cyclase generates a large number of cAMP, and one cAMP activates one protein kinase A (???). But, one protein kinase A can catalyze hundreds of reactions, therefore having an amplifying effect.
Describe the specific steps in the activation of the PIP2-calcium signal mechanism.
Another signal transduction pathway mechanism thing
- Hormone-receptor binding → G protein activation → dissociated alpha subunit from beta-gamma dimer activates phospholipase C (PLC, membrane bound enzyme)
- Phospholipase C catalyzes hydrolysis (aka splits) of PIP2 (a plasma membrane phospholipid) into 2 second messengers: DAG and IP3
- DAG activates protein kinase C which phosphorylates proteins (esp those associated with Ca2+ ion channels), therefore triggering responses within the target cell. IP3 releases Ca2+ from intracellular storage sites (smooth ER and mitochondria)
- Ca2+ is released into the cytoplasm, where it combines with intracellular proteins (e.g. calmodulin) to induce and amplify intracellular effects (Ca2+ basically takes on role of second-messenger)
Name and identify the location of the second messengers of the PIP2-calcium signal mechanism.
DAG - stays in plasma membrane
IP3 - starts in plasma membrane but can diffuse and move through cytoplasm
Identify the three types of stimuli that regulate endocrine gland secretion.
Humoral stimulus (hormone release caused in direct response to altered blood levels of certain critical ions or nutrients)
Neural stimulus (hormone release caused by neural input from nerve fibers)
Hormonal stimulus (hormone release caused by hormones produced by other endocrine organs (a tropic hormone))
Give an example of negative feedback control of hormone secretion.
A good example of negative feedback is with the hormone, insulin. Insulin is produced by the pancreas. Insulin is released by the pancreas in response to consumption of glucose. The amount of glucose in the blood rises and the pancreas detects this increase. It then secretes insulin into the blood. Insulin increases glucose uptake in target cells. Some glucose is used by the cells but some is also converted to and stored in the form of glycogen. Glucose uptake by cells decreases blood glucose levels - this decrease is detected by the pancreas and in response, it stops secreting insulin into the bloodstream. As insulin levels in the blood decrease, as does glucose uptake by cells.
