Endocrine Glands

General Information on Endocrine Glands

• The nervous system (NS) and the endocrine system (ES) work together to coordinate bodily functions and maintain homeostasis.
• The NS uses nerve impulses and neurotransmitters for rapid responses.
• The ES uses hormones for slower but longer-lasting effects.
• Both systems regulate metabolism, behavior, growth, and reproduction to meet internal and external needs.
• Homeostasis is maintained through constant temperature, pH, and ion concentration.

Endocrine System Functions

• Nutrients are processed via the digestive, respiratory, and circulatory systems.
• The body relates to its environment using the senses, coordination systems (ES & NS), and the musculoskeletal system.
• Reproduction occurs

Glands Defined

• Glands make and release substances like saliva, sweat, hormones, and tears that are needed for the body to work right.
• These substances regulate functions or eliminate waste.
• The endocrine system consists of endocrine glands that produce hormones.

Glands as Universal Producers

• Organs can be glands because they release hormones, enzymes, neurotransmitters, etc, which allow communication with other organs and tissues for homeostasis.

Glandular Structure

• Glands are made of glandular epithelial tissue.

Types of Glands

• Endocrine glands release substances within the body.
• Exocrine glands use ducts to transport substances outside the body:
  • Holocrine glands release substances when the entire secretory cell is destroyed.
  • Merocrine glands release substances without cellular damage.
  • Apocrine glands release substances with some cellular membrane material.
• Mixed glands have both endocrine and exocrine functions.

Endocrine Gland Characteristics

• They have no ducts.
• They release contents into the bloodstream or extracellular fluid.
• Cells are grouped in clusters, cords, and follicles.
• They're highly regulated by the nervous system.
• They're heavily vascularized with fenestrated vessels for substance release.
  • Fenestration allows quick passage into lymph, blood, & extracellular fluid.
• Examples:
  • Pancreatic islets (clusters)
  • Adrenal gland (cords)
  • Thyroid follicles (follicles)

Organs Secreting Hormones

• Placenta, kidney, heart, stomach, small intestine and adipocytes secrete hormones.

Chemical Messages Basics

• Chemical messengers facilitate communication among cells.

Types of Chemical Messengers

• Neurotransmitters, paracrine, autocrine, neuroendocrine, endocrine hormones, and cytokines are all chemical messengers

Cellular Communication Types

• Local and distant modes of communication are used by cells.

Local Communication Types

• Autocrine:
  • A cell communicates with itself.
  • All cells have same receptor expressions
  • Communication happens within single tissue.
• Paracrine:
  • Different kinds of cells can communicate with each other
  • One cell has the specific hormone recceptor
  • One cell makes a hormone to stimulate a different cell type.
• Intracrine:
  • A cell stimulates itself internally, without secretion.

Yuxtacrine Communication

• Receptor-mediated:
  • A cell presents a ligand on its surface
  • Another cell has complementary receptor.
  • Ligand-receptor binding starts internal signals.
  • Direct contact is needed.
  • Immune system uses this.
• Gap Junction-mediated:
  • Cells use protein bridges for communication
  • Permits passage of substances
  • Epithelial system uses this method

Distant Communication

• Nervous signaling is communication between physically separated neurons using neurotransmitters.
• Endocrine signaling happens between two cells using hormones that are released into the bloodstream
• Neuroendocrine is when a neuron communicates with a gland.

Hormone Defined

• Hormones are substances or chemical messengers secreted by a cell or group of cells into the blood and transported to a target cell where they have an effect.
• They can activate, stop, speed up, or slow down many body processes.
• Hormones can also affect their own organs/tissues or tissues.
• Hormones control metabolism, hydroelectrolytic balance, reproduction, and behavior.

Hormone Classification - Structure

• Amines/Tyrosine Derivatives
• Polypeptides/Proteins
• Steroids

Secreted Hormone Structure & Traits

• Tyrosine derivatives:
  • Thyroid hormones (T3, T4) is fat-soluble
  • Catecholamines (adrenaline, noradrenaline) are water-soluble
  • Thyroid hormones are stored extracellularly in thyroid follicles as part of thyroglobulin.
  • Thyroid hormones act by binding to intracellular receptors.
• Polypeptides/proteins:
  • They are water-soluble
  • Synthesized on rough endoplasmic reticulum (RER)
  • The ER makes prepohormones which are escinded, non bio active, and turned to smaller prohormones, contained in vesicles
  • Within a vesicle proteolitic enzyme processes a prohormone into hormone & inactive fragments.
  • Stored in cytoplasm until signal is received. - - Released upon signal.
• Steroid hormones:
  • Synthesized with cholesterol on smooth ER
  • Released just after synthesis due to fat solubility
  • Most cholesterol is from the blood

Amines: thyroid gland

• Follicles here are closed and filled with colloid
• Simple cuboidal epithelial cells secrete the colloid
• Colloid is tiroglobulin, stores tiroid hormones that cover bodily need 2-3 months
• Tirosine and thiroxine are separated from tiroglobulin to be secreted into blood
• Tiroxine & tirosine are bound by plasma proteins in blood for transport
• Combine with intraceular receptors

Fate of Circulating Catecholamines

• Are stored as hormones inside secretion vesicles until exocytosis

Regulation of Hormone Levels

• Hormone levels are regulated by secretion and metabolic elimination rates.
• Secretion: More hormone release leads to higher concetrations of hormone.
• Elimination:
  • Kidney & liver influence on elimination from bodies, increasing rate would decrese hormones.
  • Kidneys (filtration), liver (metabolism)

Hormone Clearance

• This is the rate at which hormones are removed from the blood and extracellular fluid.
• Metabolism by the kidneys or liver influences hormone elimination.

Hormone Clearance - Mechanisms

• Metabolic destruction by tissues
• Binding with the tissues
• Hepatic excretion into the bile
• Renal excretion into the urine
• Metabolism can occur in acting cell or is broken down by enzymes.

Hormone Characteristics Explained

• Half-life:
  • Rate of decline in plasma hormone
  • Peptide & catecholamines are fast dissolved
  • Steroid adrenal have semi life of ~ 20-100 min
  • thyroids are bound by blood and take hours/days to leave circulation
• Solubility affects transport:
  • H2O bound loosely or free and passes easily through cellular memebrane
  • water avoid

Hormone Transport: Water-Soluble

• Dissolve in plasma and travel directly to target tissue

Hormone Transport: Lipid-Soluble

• Bind to plasma proteins, extending half-life but only a free hormone is biological

Structure of Hormones

• Glands receive stimulus.
• Hormones are produced and pass to blood.
• Hormones are carried to all body cells.
• Hormones only work on target cells if receptors are present on or inside cell.
• Hormone binds on receptor, activating cell for function.

Cells With No Receptors

• No cellular reaction.
• Need to be a receptor with correct ligand.

Hormone Receptors

• Proteins have speciffic binding sites
• hormone-receptor binding causes cellular changes.
• Each cell has around 2000 to 100000 proteins.

Receptor Characterics

• Specific- may or may not be exclusie to hormone
• Concentratio- hormone prefernces are based on concentrato
• Saturated
• regulate & inhibit signals in multiple methods

Receptor Regualation

• internalizatio
• express upon membrane
• express in de gridatoin
• all cell need

Localized Receptor

• Receptor in or after cells
• Extracellular: on surface, speciaal with proteins/peptides bc these stay put
• Units bound use canals & activate with GPCR

Action of G-Protein Coupled Receptors (GPCR) PE

1. Inactive State

• The G protein is bound to the receptor in its inactive state. The alpha subunit has GDP bound.

2. Binding of Ligand

• The hormone binds to the domain, and causing a change in the same.

3. Activating of protein G

• This change facilitates of GDP by GTP on a subunit.

4. Deactivation of trimeric compund

• Separate from subunits, and subunit activates cellular proteins.

5. The subunit activates various protein, starting a cellular cascade.
6. Signal is sent

• The signal subunit acti protein e

7. End of signal

• hydrolyze to gdp & inactiates the subunit to recombine the complex

7. restoration of based on state

Tyrosine Jak-Stat

• Hormone by change to receptor.
• Active jack is phosphorylated to strat protetins.
• Activates gen tranport, prodecing new proteins

Enzymes - Adenyly Cyclase

• By transmebane receptor with change
• Active cell act with amp
• Amps effect activity, start protein cascade

Cells with Receptor

• On top/ in side
• Can trasn gene
• Bond ptoreis
• Ligands can easyly traverse

Localization of Intercellular Receptors

• In cel. for steoris (suprareales/ gonals) or nucleis for tireids

Structure Chart

• 3 hormns w/ chemisty for cells with no membrane -Hormones activate by cell

Gs Protein: Hormone Binding

• Binding hormone makes confirm chafe and makes protein bond

Actions: Autocrine PE

• Hormones can create cell division

Actions: Pcrine

• Secret by blood to neigbors

Actions: Endocrine

• Hormones work through cells by the circlatory or lanfic syste

Functions - Hormone Production

• Hormones production works throughout body, depending on the chemical type of chemical present
• Protein- alters permeably
• alter cell- synthesis of inter chemical
• can increase/ decrease amp & activate

Receptor types

• Intrasel have great use
• all action in protetins
• not easy cross.

Backwards Feed - Secreton

• Hormoone inhibirits protuciton on hormone by the cell
• Prevents over activitu

Secretion: Hyper/ Hypo -Thyroid

• Low throis -> TRH -? SECTSH -active, high-> inbitit TRH and TSH
• high gly -> insulin

Retro feed- positive

• The hormone inducues further secrition by it self
• Works in phases

Types of Receptor & Hormone Action

• Type- H2O avoid
• Type 2 Polar- high H2O needs transport, has short time by the recpet is membrn
• Type- type autroci/ pareci & enco

Adrenal: Amines & Secretion

• H2O avoids cells and pass

Thyroid

• Steriods

End

• all peptides

Parathori

all in peptides, glucagon (P)

Glan Sex

• tester- steoid
• Overi-> steroid

Human Chorionic Gonotropin PE

• Peptides- stimulate grouth PE

Hypothaiomas

• act for peptidos

Pitutity- Adrenos

• release peptide ex- throtropic, corcotropic, growth, proactin PE