17.10 Organs with Secondary Endocrine Functions
4 min read•june 18, 2024
The isn't just about dedicated glands. Many organs play a secondary role in hormone production, contributing to the body's complex chemical messaging network. These organs, including the , gut, and , secrete that regulate vital functions.
Beyond organs, other tissues like bone, fat, and also have endocrine roles. They produce hormones that influence metabolism, energy balance, and calcium regulation. This widespread hormone production highlights the interconnected nature of the body's regulatory systems.
Organs with Secondary Endocrine Functions
Endocrine System Overview
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- The endocrine system consists of glands and organs that produce and secrete hormones
- Hormones are chemical messengers that regulate various physiological processes
- is maintained through hormone actions on
- Target cells have specific that recognize and respond to hormones
- Feedback mechanisms (negative feedback and ) control hormone release and effects
Hormones from secondary endocrine organs
- Heart secretes hormones that regulate blood pressure and volume
- released by when blood volume and pressure increase, promoting sodium and water excretion by the kidneys (natriuresis and diuresis) to reduce blood pressure and volume
- (BNP) secreted by in response to increased ventricular pressure and volume, having similar effects as ANP on natriuresis, diuresis, and blood pressure regulation
- produces hormones that control digestion and appetite
- released by in the stomach and duodenum, stimulating gastric acid secretion, gastric motility, and growth of the gastric mucosa (lining)
- secreted by in the duodenum when acidic chyme enters, stimulating bicarbonate release from the pancreas and bile secretion from the while inhibiting gastric acid secretion and motility
- released by in the duodenum and jejunum in response to fatty acids and amino acids, stimulating pancreatic enzyme secretion, gallbladder contraction, and promoting satiety (fullness) to reduce food intake
- Kidneys secrete hormones that regulate red blood cell production and blood pressure
- (EPO) produced by when oxygen levels are low (hypoxia), stimulating red blood cell production (erythropoiesis) in the bone marrow
- released by when renal perfusion pressure decreases or sympathetic stimulation occurs, activating the ###-Angiotensin-Aldosterone_System_0### (RAAS) which leads to increased blood pressure and volume through the actions of angiotensin II and aldosterone
Endocrine roles of non-glandular tissues
- contributes to endocrine regulation through hormones secreted by bone cells
- released by during bone formation, promoting insulin secretion and sensitivity to enhance glucose homeostasis while also stimulating testosterone production in the testes
- (FGF23) secreted by and osteoblasts when serum phosphate levels rise, reducing phosphate reabsorption in the kidneys and inhibiting the synthesis of active (1,25-) to regulate phosphate and vitamin D balance
- secretes hormones that regulate energy balance and metabolism
- released by in proportion to fat stores, acting on the hypothalamus to suppress appetite and increase energy expenditure, regulating long-term energy balance and body weight
- secreted by , with levels inversely related to body fat percentage, enhancing insulin sensitivity and glucose uptake in target tissues while possessing anti-inflammatory and cardioprotective properties
- Skin synthesizes vitamin D, a hormone that regulates calcium and phosphate balance
- Vitamin D produced in the skin when exposed to ultraviolet B (UVB) radiation, then converted to its active form (1,25-dihydroxyvitamin D) in the liver and kidneys, regulating calcium and phosphate homeostasis to promote bone mineralization while also modulating immune function and cell differentiation
Thymus vs liver hormone functions
- secretes hormones that support T lymphocyte development and immune function
- released by , stimulating the differentiation and maturation of T lymphocytes to enhance cell-mediated immunity
- secreted by thymic epithelial cells, promoting T lymphocyte differentiation and function while modulating immune responses and inflammation
- Liver produces hormones that regulate growth, metabolism, and blood pressure
- (IGF-1) secreted by when stimulated by growth hormone, promoting cell growth, differentiation, and survival in various tissues while regulating glucose and lipid metabolism to enhance insulin sensitivity
- released by and cleaved by renin to form angiotensin I, serving as a precursor to angiotensin II (a potent vasoconstrictor and aldosterone stimulator) as part of the renin-angiotensin-aldosterone system (RAAS) that regulates blood pressure and volume
- secreted by hepatocytes and kidney cells, stimulating megakaryocyte differentiation and platelet production in the bone marrow to regulate platelet count and hemostasis (blood clotting)
Key Terms to Review (61)
Adipocytes: Adipocytes, also known as fat cells, are specialized cells within the body that store energy in the form of fat. They play a crucial role in energy balance, insulation, and cushioning of vital organs.
Adipocytes: Adipocytes, also known as fat cells, are specialized cells that store energy in the form of lipids. They play a crucial role in the body's connective tissue and endocrine functions.
Adiponectin: Adiponectin is an adipokine, a hormone secreted by adipose (fat) tissue, that plays a crucial role in regulating metabolism and energy balance. It is involved in various physiological processes, including glucose and lipid homeostasis, insulin sensitivity, and inflammation.
Adipose Tissue: Adipose tissue, also known as fat tissue, is a type of connective tissue composed primarily of adipocytes (fat cells). It serves important functions in the body, including energy storage, insulation, and endocrine signaling. Adipose tissue plays a crucial role in maintaining homeostasis, supporting various organ systems, and contributing to the overall health and well-being of the individual.
Angiotensinogen: Angiotensinogen is a precursor protein produced by the liver that plays a critical role in blood pressure regulation and fluid balance in the body. It is converted into angiotensin I by the action of renin, an enzyme released by the kidneys.
Angiotensinogen: Angiotensinogen is a glycoprotein precursor produced primarily by the liver that is cleaved by the enzyme renin to form angiotensin I, a key component of the renin-angiotensin-aldosterone system (RAAS) which regulates blood pressure and fluid balance in the body.
Atrial Cardiomyocytes: Atrial cardiomyocytes are the contractile muscle cells that make up the walls of the atria, the upper chambers of the heart. These specialized cardiac muscle cells play a crucial role in the secondary endocrine functions of the heart, contributing to the regulation of various physiological processes in the body.
Atrial Natriuretic Peptide: Atrial natriuretic peptide (ANP) is a hormone produced primarily by the atria of the heart. It plays a crucial role in the homeostatic regulation of the vascular system and is also considered a secondary endocrine function of the heart.
Atrial natriuretic peptide (ANP): Atrial natriuretic peptide is a hormone secreted by the heart's atria that regulates blood pressure and fluid balance. It lowers blood pressure by causing the kidneys to excrete more sodium and water, thus reducing blood volume.
Brain Natriuretic Peptide: Brain natriuretic peptide (BNP) is a hormone produced primarily by the ventricles of the heart. It is released in response to increased ventricular volume and pressure, and it helps regulate fluid and electrolyte balance in the body by promoting natriuresis (increased sodium excretion) and diuresis (increased urine output).
Brown adipose tissue: Brown adipose tissue (BAT) is a type of fat found in the body that generates heat to help maintain body temperature in cold environments and during the neonatal period. Unlike white adipose tissue, which stores energy, brown adipose tissue burns calories to produce warmth without shivering, a process known as thermogenesis.
Cholecystokinin: Cholecystokinin (CCK) is a peptide hormone produced by I-cells in the duodenum and jejunum of the small intestine. It plays a crucial role in the regulation of digestion, particularly in the stimulation of the gallbladder to release bile and the pancreas to secrete digestive enzymes.
Cholecystokinin (CCK): Cholecystokinin is a hormone produced by the cells of the small intestine in response to the presence of fats and proteins, which stimulates the digestion of lipids and proteins by inducing bile release from the gallbladder and enzyme secretion from the pancreas. It also slows down gastric emptying, helping in the efficient digestion of nutrients.
Development and Aging of the Endocrine System: The process by which the endocrine system evolves and changes in structure and function from birth through old age, impacting hormone production and regulation. It encompasses both the maturation of this system during childhood and adolescence, as well as its gradual decline in efficiency as part of the natural aging process.
Dihydroxyvitamin D: Dihydroxyvitamin D is a form of vitamin D that is crucial for the regulation of calcium and phosphate levels in the bloodstream, promoting healthy bone formation and maintenance. It is produced in the body through a process involving skin exposure to sunlight, liver transformation, and finally activation in the kidneys.
Endocrine System: The endocrine system is a complex network of glands and organs that produce and secrete hormones, chemical messengers that regulate various physiological processes in the body. It works in coordination with the nervous system to maintain homeostasis and ensure the proper functioning of the body's systems, including metabolism, growth, development, and reproduction.
Erythropoietin: Erythropoietin is a glycoprotein hormone produced primarily by the kidneys that stimulates the production of red blood cells in the bone marrow. It plays a crucial role in regulating erythropoiesis, especially in response to low oxygen levels in the blood, which can be caused by various factors such as high altitudes, anemia, or respiratory diseases.
Fibroblast Growth Factor 23: Fibroblast Growth Factor 23 (FGF23) is a hormone primarily produced by osteocytes in the bone that plays a crucial role in phosphate metabolism and vitamin D regulation. It acts mainly on the kidneys to promote urinary phosphate excretion and inhibit the synthesis of 1,25-dihydroxyvitamin D, thereby influencing calcium homeostasis and overall mineral balance in the body.
G Cells: G cells, also known as gastrin-producing cells, are a type of endocrine cell found primarily in the pyloric antrum of the stomach. These cells are responsible for the production and secretion of the hormone gastrin, which plays a crucial role in the digestive process and the regulation of stomach acid secretion.
Gastrin: Gastrin is a hormone produced by the stomach that stimulates the secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It plays a critical role in the digestive process by preparing the stomach to digest and absorb nutrients effectively.
Gastrin: Gastrin is a hormone produced by G cells in the stomach and duodenum that stimulates the secretion of gastric acid, which aids in the digestion of food. It is a key player in the regulation of the digestive system processes and the function of the stomach.
Gastrointestinal Tract: The gastrointestinal tract, also known as the digestive tract, is a complex system of organs responsible for the ingestion, digestion, and absorption of food, as well as the elimination of waste products. It plays a crucial role in the body's overall metabolic processes and endocrine functions.
Heart: The heart is a vital organ that functions as the central pump of the cardiovascular system, responsible for circulating blood throughout the body. It is a muscular, hollow organ that contracts rhythmically to maintain the flow of oxygenated blood to the body's tissues and deoxygenated blood to the lungs for gas exchange.
Hepatocytes: Hepatocytes are the main functional cells of the liver, responsible for carrying out a wide range of biochemical activities essential for digestion, metabolism, and detoxification. These cells play a pivotal role in processing nutrients, producing bile, and breaking down toxins.
Hepatocytes: Hepatocytes are the main functional cells of the liver, responsible for carrying out the organ's diverse metabolic and synthetic functions. As the primary cell type in the liver, hepatocytes play a crucial role in both the endocrine and digestive systems of the body.
Homeostasis: Homeostasis is the process through which the body maintains a stable internal environment despite external changes. This concept is crucial as it ensures that physiological processes function optimally, allowing for growth, reproduction, and overall health.
Hormones: Hormones are chemical messengers produced by the endocrine system that regulate and coordinate various physiological processes in the body. They play a crucial role in maintaining homeostasis, growth, development, and adaptation to changes in the internal and external environment.
I Cells: I cells, also known as interstitial cells, are a specialized type of cell found in various organs that have secondary endocrine functions. These cells play a crucial role in the regulation of hormone production and secretion, contributing to the overall endocrine system's functionality.
Insulin-like Growth Factor-1: Insulin-like Growth Factor-1 (IGF-1) is a hormone-like substance that is structurally and functionally similar to insulin. It plays a crucial role in regulating growth, development, and metabolism in the body. IGF-1 is produced primarily by the liver in response to growth hormone stimulation and has widespread effects on various tissues and organs.
Juxtaglomerular cells: Juxtaglomerular cells are specialized smooth muscle cells located in the walls of the afferent arterioles of the nephron, primarily responsible for the regulation of blood pressure and fluid balance in the body. These cells play a crucial role in the renin-angiotensin-aldosterone system, contributing to the homeostatic control of renal blood flow and systemic vascular resistance.
Kidneys: The kidneys are a pair of vital organs located in the lower back that play a crucial role in the body's overall health and functioning. They are responsible for filtering waste and excess water from the blood, regulating fluid and electrolyte balance, and maintaining acid-base balance, among other essential functions.
Layers of the Skin: The layers of the skin consist of three primary parts: the epidermis (the outermost layer), the dermis (the middle, supportive layer containing hair follicles and glands), and the hypodermis (the deeper, fatty layer that insulates and protects the body). These layers work together to protect the body from external damage, regulate temperature, and enable sensation.
Leptin: Leptin is a hormone primarily produced by fat cells that regulates energy balance by inhibiting hunger, which in turn diminishes fat storage in adipocytes. It acts on the brain's hypothalamus to communicate satiety, signaling that the body has enough energy stored.
Leptin: Leptin is a hormone produced primarily by adipose (fat) tissue that plays a crucial role in regulating energy balance, appetite, and metabolism. It acts on the central nervous system, particularly the hypothalamus, to signal the body's energy status and influence feeding behavior and energy expenditure.
Leydig cells: Leydig cells are specialized cells located in the testes that produce testosterone, a crucial hormone for the development of male secondary sexual characteristics and reproductive functions. These cells respond to luteinizing hormone signals by synthesizing and releasing testosterone into the bloodstream.
Liver: The liver is a vital organ in the body that plays a crucial role in various metabolic processes, including the digestive system, endocrine functions, and protein metabolism. It is the largest internal organ and is located in the upper right part of the abdomen, just behind the ribcage.
Osteoblasts: Osteoblasts are specialized bone cells responsible for the formation and mineralization of bone tissue. They play a crucial role in the growth, maintenance, and repair of the skeletal system, as well as in calcium homeostasis throughout the body.
Osteocalcin: Osteocalcin is a non-collagenous protein found in bone that is involved in the mineralization and regulation of bone tissue. It is considered a marker of bone formation and plays a crucial role in the overall health and development of the skeletal system.
Osteocytes: Osteocytes are the most abundant cells found in mature bone tissue. They are derived from osteoblasts and play a crucial role in the structure, function, and maintenance of the skeletal system across various physiological contexts.
Peritubular Capillary Endothelial Cells: Peritubular capillary endothelial cells are specialized cells that line the walls of the peritubular capillaries, which are the blood vessels surrounding the renal tubules in the kidneys. These cells play a crucial role in the secondary endocrine functions of the kidneys.
Positive feedback: Positive feedback is a process in physiology where an initial stimulus is amplified, leading to an increased response. This mechanism moves the body away from its baseline state and is often involved in rapid changes.
Positive Feedback: Positive feedback is a self-reinforcing mechanism in biological systems where the output of a process enhances or amplifies the initial input, leading to a continued increase in the system's response. This type of feedback loop contrasts with negative feedback, which acts to stabilize and maintain homeostasis within the body.
Receptors: Receptors are specialized protein molecules located on the surfaces of cells that bind to specific signaling molecules, such as hormones or neurotransmitters, triggering a cellular response. They play a crucial role in communication within the body, helping to regulate physiological processes by responding to various stimuli from the internal and external environment.
Renin: Renin is an enzyme secreted by the juxtaglomerular cells of the kidneys in response to low blood pressure or decreased sodium chloride concentration. It plays a critical role in the body's regulation of blood pressure, electrolyte balance, and fluid volume.
Renin: Renin is an enzyme produced by the kidneys that plays a crucial role in the regulation of blood pressure and fluid balance within the body. It is a key component of the renin-angiotensin-aldosterone system, which is responsible for maintaining homeostasis in the cardiovascular and renal systems.
Renin-Angiotensin-Aldosterone System: The renin-angiotensin-aldosterone system (RAAS) is a complex hormonal cascade that plays a crucial role in regulating blood pressure, fluid balance, and electrolyte homeostasis within the body. It is a key component in the homeostatic regulation of the vascular system, the physiology of urine formation, and the overall maintenance of fluid volume and composition.
S Cells: S cells, also known as somatostatin-secreting cells, are a type of endocrine cell found in various organs that have secondary endocrine functions. These cells produce the hormone somatostatin, which plays a crucial role in regulating the secretion of other hormones and maintaining homeostasis within the body.
Secretin: Secretin is a hormone produced by the S cells of the duodenum that stimulates the pancreas to release bicarbonate-rich fluids, essential for neutralizing stomach acid in the small intestine and aiding in protein digestion. It plays a pivotal role in regulating the pH of the intestinal environment to optimize enzyme activity for nutrient absorption.
Secretin: Secretin is a peptide hormone produced by the S-cells in the duodenum and upper jejunum of the small intestine. It plays a crucial role in the regulation of digestion and the function of the pancreas, liver, and stomach.
Skeleton: The skeleton is the internal framework of bones and cartilage that provides structure, support, and protection for the body. It serves as the attachment point for muscles and tendons, facilitating movement, and also plays a crucial role in the body's endocrine functions.
Skin: Skin is the largest organ of the human body, serving as a protective barrier against the external environment. It is a complex structure composed of multiple layers and specialized cells that perform a variety of essential functions, including regulating body temperature, providing sensation, and producing vitamin D.
Target cells: Target cells are specific cells that possess receptors for particular hormones, allowing them to respond to those hormones' signals. The interaction between hormones and target cells is crucial for the regulation of various physiological processes, as only cells with the appropriate receptors can be affected by specific hormonal messages.
Thrombopoietin: Thrombopoietin is a hormone produced primarily by the liver and kidneys that regulates the production of platelets by the bone marrow. It plays a crucial role in maintaining normal platelet counts in the bloodstream, which are essential for blood clotting and wound healing.
Thrombopoietin: Thrombopoietin is a glycoprotein hormone that primarily stimulates the production and maturation of platelets, also known as thrombocytes, from megakaryocytes in the bone marrow. It is a key regulator of platelet production and plays a crucial role in maintaining normal blood clotting and hemostasis.
Thymic Epithelial Cells: Thymic epithelial cells are a specialized type of cells found in the thymus gland, which is an organ with secondary endocrine functions. These cells play a crucial role in the development and maturation of T cells, a vital component of the adaptive immune system.
Thymosin: Thymosin is a hormone produced by the thymus gland, which is a small organ located in the upper chest. Thymosin plays a crucial role in the development and function of the immune system, particularly in the maturation and differentiation of T cells, a type of white blood cell essential for cell-mediated immunity.
Thymulin: Thymulin is a hormone produced by the thymus gland, a secondary endocrine organ that plays a crucial role in the development and regulation of the immune system. As a key component of the neuroendocrine-immune axis, thymulin helps coordinate the body's response to various stimuli and maintain homeostasis.
Thymus: The thymus is a small, lobulated organ located in the upper anterior portion of the chest cavity, crucial for the development and maturation of T-lymphocytes (T cells), which are essential components of the adaptive immune system. It gradually shrinks after puberty, but its early-life function is critical for establishing a robust immune defense.
Thymus: The thymus is a small, bilobed organ located in the upper chest, just behind the breastbone. It plays a crucial role in the development and functioning of the immune system, particularly in the maturation and differentiation of T lymphocytes, a type of white blood cell essential for adaptive immunity.
Ventricular Cardiomyocytes: Ventricular cardiomyocytes are the specialized muscle cells that make up the walls of the ventricles, the lower chambers of the heart. These cells are responsible for the powerful contractions that pump blood out of the ventricles to the lungs and body, playing a crucial role in the heart's secondary endocrine functions.
Vitamin D: Vitamin D is a fat-soluble vitamin that plays a crucial role in maintaining bone health, calcium homeostasis, and various other physiological processes in the body. It is often referred to as the 'sunshine vitamin' because the human body can synthesize it when the skin is exposed to ultraviolet B (UVB) radiation from sunlight.
Vitamin D is closely linked to the topics of bone formation and development, exercise, nutrition, and calcium homeostasis. It also has important interactions with the parathyroid glands, organs with secondary endocrine functions, chemical digestion and absorption, and overall nutrition and diet.