Endocrine System: Glands, Organs, and Hormones

• Endocrine glands are formed by groups of secretory cells surrounded by connective tissue that provides them with blood vessels, lymphatic capillaries, and nerves
• The secretory gland is constituted by specialized epithelium that has been modified to produce secretions and secreted products (hormones) pass into the extracellular space around the secretory cells

Endocrine Gland

• The human body includes the following glands:
  • pituitary gland
  • thyroid gland
  • parathyroid gland
  • adrenal glands
  • pineal gland

Endocrine Organs

• Endocrine tissues do not consist of a gland
  • hypothalamus
  • thymus
  • heart
  • pancreas
  • stomach
  • liver
  • small intestine
  • kidneys
  • ovaries
  • testicles
  • placenta
  • cells in adipose tissue or blood (lymphocytes)

Hormones

• A chemical substance secreted by a group of cells, which exerts physiological effects on other cells of the organism
• Local hormones act near their site of release

Paracrine

• Affects neighboring cells

Autocrine

• Acts on the same cell that secretes it

General Hormones

• Diffuse from the extracellular space into the capillaries and are transported by the blood to all tissues of the body

Target Cell

• An organ cells, gland, and tissue, hormones reach it to perform a function, possesses specific receptors.

Type of Hormone According to Chemical Structure

Steroid Hormones

• Chemical structure is similar to cholesterol and are synthesized in the smooth endoplasmic reticulum of endocrine cells, structure varies according to the collateral chemical groups, allows them to exert different effects.
• Secreted by:
  • Adrenal Cortex → Cortisol, aldosterone
  • Ovary → Estrogens and progesterone
  • Testicle → Testosterone

Biogenic Amines

• Derived from the amino acid tyrosine and simple hormonal molecules.
• Secreted by:
  • Thyroid gland → Thyroxine and triiodothyronine
  • Adrenal Medulla → Adrenaline and noradrenaline, a neurotransmitter that can exit the central nervous system and produce a physical effect
  • Pineal Gland → Melatonin
• Other amines: histamine, derived from the amino acid histidine, is secreted by mastocytes and platelets. Serotonin, derived from the amino acid tryptophan, is secreted by basophils and platelets

Protein or Peptide

• Derived from chains of amino acids and are synthesized in the rough endoplasmic reticulum of endocrine cells
  • Hypothalamus → releasing and inhibiting hormones that act on the secretion of the adenohypophysis
  • Adenohypophysis → Thyrotropin, corticotropin, gonadotropin, growth hormone, and prolactin
  • Neurohypophysis → Antidiuretic hormone and oxytocin
  • Thyroid Gland → Calcitonin
  • Endocrine Pancreas → Insulin, glucagon, and somatostatin
  • Parathyroid Gland → Parathormone
  • Digestive System → Digestive hormones like gastrin, secretin and others

Eicosanoids

• Derived from arachidonic acid
• Two main types: prostaglandin and leukotrienes, secreted by all cells except erythrocytes

Production and Storage of Hormones

Steroid Hormones

• Glandular cells contain precursor molecules like cholesterol and intermediate molecules
• After stimulation, enzymes rapidly convert these compounds into final hormones
• They are secreted immediately

Biogenic Amine Hormones

• Adrenaline and noradrenaline are formed by the action of enzymes in the cytoplasm of glandular cells and stored in vesicles until secreted
• Thyroid hormones: Thyroglobulin is stored within the thyroid gland, stimulation triggers various enzymatic systems within the glandular cells, enzymes break down the thyroglobulin molecule and allow active hormone to be released into the blood.

Protein Hormones

• Preprohormone is an immature form derived from messenger RNA, packaged in the Golgi apparatus, processed, and stored in secretion granules until a specific signal stimulates its release, leading to the definitive hormone

Initiation of Hormonal Secretion

Rapid Secreted Hormone

• Adrenaline and noradrenaline: initiates hormonal secretion through stimulation of the sympathetic nervous system in one second and reach maximum activity in one minute

Very Slow Secreted Hormone

Thyroid Hormone: begins after stimulation, requires months before the final secretion occurs, taking hours or days before activity starts, and its effect can last 4-6 weeks

• Each hormone has different initiation and duration; not all have the same secretion start."

Classification

Hormone Transport in Blood

• Endocrine glands are highly vascularized organs
  • Water-soluble hormones circulate freely in the plasma e.g. adrenaline and noradrenaline, peptides-proteins
  • hydrophobic hormones (steroids and thyroid) are transported bound to specific liver proteins like globulin binder

Functions

• Improves the transportability of hydrophobic hormones
• Delays the loss of small molecules of hormones by filtration through the kidney and their exit from the organism through urine
• Provides a reserve of hormone in the blood

Mode of Action of Hormones

• Response to a hormone varies depending on the target cell
• Insulin stimulates glycogen in the liver and triglycerides in adipocytes
• Hormones affect
  • synthesis
  • transport
  • muscle contraction
  • permeability
  • metabolism

Activation of Intracellular Receptors

• Steroid and thyroid hormone: readily enter the plasma membrane, intracellular receptors are receptors inside the cell that receive the hormone, generating deposit of information, its hormone encodes it within the nucleus, enters DNA and messenger RNA generates the function

Activation of Plasma Membrane Receptors

• Adrenaline, noradrenaline, peptides and proteins: first messenger, cannot enter within the membrane because they are water-soluble
• Receptors are located on the external surface of the plasma membrane, only transmit the message to the membrane
• Cyclic AMP (cAMP), Calcium, or inositol triphosphate are second messengers, it carries the message inside the cell
• Hormone binds to receptor, activates protein G, activates adenyl cyclase, enzyme that synthetizes cyclic AMP from ATP
• Function facilitates hormonal responses but does not directly produce a physiological response

Hormonal Interactions

• Target cell response to a hormone depends on the concentration of the hormone and the number of receptors also interacts with other hormones.
• Permissive effect is where the effect of one hormone on a target cell requires prior or simultaneous exposure to another hormone/s
• Examples: Elevated estrogen level can increase the number of progesterone receptors, preparing the uterus for the implantation of a fertilized ovum

Synergistic Effect

• Two or more hormones complement their respective actions and both are necessary to achieve the total hormonal response.
• Example: Milk production and release in mammary glands requires combined action of estrogen, progesterone, prolactin and oxytocin

Antagonistic Effect

• Effect of one hormone on a target cell is counteracted by another hormone.
• Example: Insulin reduces blood glucose levels, while glucagon increases them

Regulation of Hormone Secretion

• Hormones released in short bursts with little or no secretion between bursts. When stimulated, endocrine glands will release hormones more frequently, increasing blood levels of the hormone."

Neural Signals

• Changes in blood chemistry
• Other hormones

Mechanisms

• Negative feedback is most present and frequent, representing 90% of the feedback mechanisms utilized by almost all hormones. A - Glucagon increases glucose levels in the blood
• Hormone A increases the concentration of substrate B in plasma
• Increased blood glucose triggers a signal to glucagon, glucagon no longer increases
• High levels of substrate B will inhibit the secretion of hormone A
• Glucagon stops increasing glucose, starts to decrease, and glucagon increases
• Decrease of substrate B stimulates the secretion of hormone A

Positive Feedback

• Positive feedback (feedback positive) contributes to regulation of hormonal secretion
• An example occurs during childbirth, oxytocin stimulates uterine contractions, uterine contractions further stimulate oxytocin release
• In positive feedback, response produced by hormone intensifies the initial stimulus
• Secretion of several hormones follow environmental cycles like light/darkness or sleep/wake cycles
• 24-hour are known as circadian rhythms. Secretion of various hormones follows circadian rhythms

Endocrine Pancreas

• Exocrine Function → Produces digestive secretions, secreted into the duodenum
• Endocrine Function → Produces secretions in islets of Langerhans.

Islets of Langerhans

• Vascularized and innervated by sympathetic and parasympathetic fibers of the autonomic nervous system.
• Types of cells:
  • Alpha cell secretes glucagon → Important due to being more competent in regulating blood glucose levels
  • Beta cell secretes insulin
  • Delta cell secretes somatostatin → Has a function where it can interact with glucagon and insulin Insulin is a polypeptide of 51 amino acids produced by the beta cells of the islets of Langerhans, it is linked to B-globulin.

Metabolic Effect

• Stored in granules and released into the blood of the portal vein, reaching high concentrations in the liver, acts on muscle and adipose tissue.
• Binds to cellular receptors, stimulating the insertion of glucose transporters, increasing its uptake by the cells
• Half-life in plasma is approximately 5 minutes, rapidly captured by the liver, kidneys, muscles, and adipose tissue
• A small amount is eliminated through urine

Effect of Insulin

• Protein: Promotes the transport of amino acids into cells, stimulates protein synthesis, reduces catabolism, promoting protein storage, acts synergistically with the growth hormone for cell growth
• Lipids: Increases lipogenesis with conversion of glucose or other nutrients into fatty acids increases the storage of triglycerides in adipose tissue
• Carbohydrate acts in response to high glucose levels, exerting a hypoglycemic effect by facilitating the uptake of glucose by cells, also stimulates glycogenesis and reduces glycogenolysis and gluconeogenesis

Regulation of Secretion

• Blood Glucose the main regulator. When glucose levels are low (3-4 mmol/L), almost no insulin is detected in the blood
• After a meal, glucose levels increase, and insulin secretion rises, peaking between 30-60 minutes after the meal, multiplying its basal level by 3 to 10 times
• Autonomic Nervous System: sympathetic stimulation and catecholamines reduce the insulin secretion, while parasympathetic stimulation increases it.
• Hormones: GH and cortisol induces hyperglycemia, indirectly increasing insulin secretion
• Peptide C: Released together with insulin in a 1:1 ratio, although its biological function is unknown, it is a useful marker of insulin secretion
• It is not absorbed by the liver and is excreted in the urine. Measuring its concentration in a 24-hour urine sample allows for evaluating insulin secretory capacity. Metabolism of Insulin: More than 60% of secreted insulin is absorbed by the liver before reaching systemic circulation. A half-life of approximately 6 minutes, depending on the balance between secretion and inactivation

Torrente Songuineo

• Torrente Songuíneo is at normal glucose
• The intestine absorbs after eating glucose after feeding
• After the release of glucose to the blood there will be an high increaseof glucose
• After releasing the glucose the pancrea will respond with an high increase of insulin
• After the release of insclina , it is directed the live rand other body parts to control the glucose The opposite of insulin glucagon

Glucagon - Metabolic Effects -

• Glucagon is a polypeptide of 29 amino acids synthesized and released by the alpha cells of the islets of Langerhans in the pancreas and, unlike insulin, it raises the level of glucose in the blood. That is, it is a hyperglycemic hormone. Like insulin, its lifespan in the plasma is about 6 minutes. Its main target tissue is the liver.

Effects on proteins:

• Glucagon increases hepatic uptake of some amino acids and gluconeogenesis or synthesis of new glucose from amino acids, which helps to increase glucose levels in plasma

Effects on fats:

• Increase lipolysis, mobilizing fatty acids and glycerol, the glycerol can act as a precursor of glucose in the hepatic gluconeogenesis.

Effects on carbohydrates:

• Increase of hepatic glycogenolysis and inhibits glycogen synthesis with what more amount of glucose passes to the plasma. Glycogen and is stimulates, also, arginine and alanine), as well as sympathetic and parasympathetic stimuli
• Somatostatin inhibits the release of glucagon

Glicemia

• Principal function of endocrino in the pancreas is regulatinf the glucose or glucose levels in the plasma. In a normal person the glucose level is controlled beetwen a very limite of 70 and 100 mg

Functions of pancreas

• 1.insulin is the hormona that have the cápsula to down the glicemia and the hormona is more hiperglusemiante .

The líver

• Functions is that like an amortiguador because elevate the glicemia and insulin but después of comida ( food)
• to 2/3 are absorbed and almacena in the líver in fórmate like glucosico again and more low in glicemia the hormones are liberadas so the hormone liberates glucose again

Hypothalamic-Pituitary Axis of Hipotolamo

• Pituitary (Hypophysis) is an endocrine gland that regulates multiple hormonal functions in the body
• It is located in the sella turcica and is attached to the hypothalamus through the infundibulum, they dividen in 2 forms like the Adrenohiposis 75% what way to the fisis
  • (pitucitos) are supported the células that are similares to the glías
• Hipotálamo is in estructura in nerviosa that is the base of the en céfalo that has receptors is that from the zona of the encéfalo and that is in the nerve systém what regulase the temperature así like the hambre sed conducla sexual y defensitas the Hipotálamo produces hormonce when regulase the secreción of hormone And these hormones is transported in the nervio fisis and is located en la sangre hormomese

Thyroid

• the organ located in front of the laringes
• Hipotálamo hipofisiario thyroids and liberadas
• The tiroideos makes the thyroid hormones and thyroid yodotrioxina liberadas
• Each type of adenohypophyseal hormone has the corresponding hypothalamic releasing hormone, and some also have the corresponding hypothalamic inhibiting hormone
• The hypothalamus secretes: thyrotropin-releasing hormone (TRH), which boosts prolactin, gonatropin-releasing hormone (GnRH); corticotropin-releasing hormone (CRH): the prolactin-inhibiting hormone (dopamine, PIH): the prolactin (its absence for a specific prolactin liberating hormon)
• Growth hormone-releasing hormone (GHRH): hormone inhibitor (somatostatin, GHIH) of growth hormone that can inhibit prolactin and thyrotropin and hormone inhibitor and releasere

Hormonio crecimiento

• One Hormos es Somatotropina the protecina that that are celosioes
• The GH stimulates, in all celula, the aminosidoes, the DNA, and the hormones and that stimulatite .
• Is to that the fats is released grasoses, the GH estimulase that

Regulation of growth hormone or, Somatropina

• Liberation of this gland is influenced by hormones and metabolites, so the secretion sigue and that has the 1 or 2 years durane the sueño
• Factores como estimiluan , if like , traumatismos even intense activities can estimular its liberación
• The hormone of creceimiento is regulated in the two gland hormonase
• Hormal liberators de GH ( GHRH )
• hormonal Inhibitors of (ghih )

Hipophysis Adeno

• Hormonal estimate de melonacioshs (ash )
• The melanacios that are the of the termins (8 % de the epidermis or the of elcolor de la piel and the color de the luz
• The se unal MC-1
• Is with hormonal the principal gland ma maria and is the principal órgano

Neurohypophysis

• is conectado en con el hipotálamo -hipototalmico and is conéctale with hormones the neurofibrosis that the gland only almacena and libera Esas hormonas son

The hormona son are la Oxitocina

• This gland , stimulate this gland

Hormona Antidiurética o vasopresina( ADH)

• The principal action is effect antidiurético and name hormono of diálisis and this in the riñes, this happens of ADN and aumente is de la nefrona
• What causes is the falta is causes what creates more problemas for las células so that’s causes and eluminate great volumen of diluida to exist in y los des reptadores of vasopresina

La y son of and also the what is in is the pote nte que sobre de arteroiles

• The pressure can come even the arterias that cause so that comes and the y

Glandular Tireoideas

• The glandular entre 10 y 20 and this is abajo de the se and the and is formacion for the conectados is tejido and is formada with foliculos is between y la that has and a and with the que this contiens que from Las

Síntesis Almacenados

• las hormonas tiroideas y son únicas contienen para para cantidades normales de estas hormonas se necesita ingerir semana