Neuroendocrine cells are cells that receive neuronal input (through

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

s released by nerve cells or neurosecretory cells) and, as a consequence of this input, release messenger molecules (

hormones A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physiology and behavior. Hormones a ...

) into the blood. In this way they bring about an integration between the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

and the

endocrine system The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant Organ (biology), organs. In vertebrat ...

, a process known as neuroendocrine integration. An example of a neuroendocrine cell is a cell of the

adrenal medulla The adrenal medulla () is the inner part of the adrenal gland. It is located at the center of the gland, being surrounded by the adrenal cortex. It is the innermost part of the adrenal gland, consisting of chromaffin cells that secrete catecho ...

(innermost part of the

adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer adrenal corte ...

), which releases

adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

to the blood. The adrenal medullary cells are controlled by the sympathetic division of the

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

. These cells are modified postganglionic neurons. Autonomic nerve fibers lead directly to them from the central nervous system. The adrenal medullary hormones are kept in vesicles much in the same way neurotransmitters are kept in neuronal vesicles. Hormonal effects can last up to ten times longer than those of neurotransmitters. Sympathetic

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

fiber impulses stimulate the release of adrenal medullary hormones. In this way the sympathetic division of the autonomic nervous system and the medullary secretions function together. The major center of neuroendocrine integration in the body is found in the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

and the

pituitary gland The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the human brain, brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus contr ...

. Here hypothalamic neurosecretory cells release factors to the blood. Some of these factors (

releasing hormone Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are also called liberins () and statins () (respectively), or releasing ...

s), released at the hypothalamic median eminence, control the secretion of pituitary hormones, while others (the hormones

oxytocin Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include Human bonding, ...

and

vasopressin Mammalian vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the ''AVP'' gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It ...

) are released directly into the blood. APUD cells are considered part of the neuroendocrine system, and share many staining properties with neuroendocrine cells.

Major neuroendocrine systems

Hypothalamic–pituitary–adrenal axis The hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis) is a complex set of direct influences and feedback interactions among three components: the hypothalamus (a part of the brain located below the thalamus), the pituitary gland ( ...

(HPA axis) * Hypothalamic–pituitary–thyroid axis (HPT axis) * Hypothalamic–pituitary–gonadal axis (HPG axis) * Hypothalamic–neurohypophyseal system

Pulmonary neuroendocrine cells

Pulmonary neuroendocrine cells (PNECs) are specialized airway epithelial cells that occur as solitary cells or as clusters called neuroepithelial bodies (NEBs) in the

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

. Pulmonary neuroendocrine cells are also known as ''bronchial'' Kulchitsky cells. They are located in the

respiratory epithelium Respiratory epithelium, or airway epithelium, is ciliated pseudostratified columnar epithelium a type of columnar epithelium found lining most of the respiratory tract as respiratory mucosa, where it serves to moisten and protect the airways ...

of the upper and lower

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirato ...

. PNECs and NEBs exist from

fetal A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a ...

and neonatal stages in the lung airways. These cells are bottle- or flask-like in shape, and reach from the

basement membrane The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tis ...

to the lumen. They can be distinguished by their profile of bioactive amines and peptides, namely

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

calcitonin Calcitonin is a 32 amino acid peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid (or endostyle) in humans and other chordates in the ultimopharyngeal body. It acts to reduce blood calcium (Ca2+), opposing the ...

calcitonin gene-related peptide Calcitonin gene-related peptide (CGRP) is a neuropeptide that belongs to the calcitonin family. Human CGRP consists of two Protein isoform, isoforms, CGRP alpha (α-CGRP, also known as CGRP I) and CGRP beta (β-CGRP, also known as CGRP II). α-C ...

(CGRP), chromogranin A, gastrin-releasing peptide (GRP), and cholecystokinin. These cells can be the source of several types of lung cancer, most notably small cell carcinoma of the lung, and bronchial carcinoid tumor.

Function

PNECs may play a role with chemoreceptors in hypoxia detection. This is best supported by the presence of an oxygen-sensitive potassium channel coupled to an oxygen sensory protein in the rabbit lumenal membrane. They are hypothetically involved in regulating localized epithelial cell growth and regeneration through a paracrine mechanism, whereby their signaling peptides are released into the environment. In addition, they contain neuroactive substances which are released from basal cytoplasm. These substances induce autonomic nerve terminals or vasculature in the deep

lamina propria The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital ...

Role in fetal lung

In the fetal lung, they are frequently located at the branching points of airway tubules, and in humans are present by 10 weeks gestation. Peptides and amines released by PNEC are involved in normal fetal lung development including branching morphogenesis. The best-characterized peptides are GRP, the mammalian form of bombesin, and CGRP; these substances exert direct mitogenic effects on epithelial cells and exhibit many properties akin to growth factors.

Example

Specialized groups of neuroendocrine cells can be found at the base of the

third ventricle The third ventricle is one of the four connected cerebral ventricles of the ventricular system within the mammalian brain. It is a slit-like cavity formed in the diencephalon between the two thalami, in the midline between the right and lef ...

in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

(in a region called the

). This area controls most

anterior pituitary The anterior pituitary (also called the adenohypophysis or pars anterior) is a major Organ (anatomy), organ of the endocrine system. The anterior pituitary is the glandular, Anatomical terms of location#Usage in human anatomy, anterior lobe that t ...

cells and thereby regulates functions in the entire body, like responses to stress, cold,

sleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain Sensory nervous system, sensory activity is inhibited. During sleep, there is a marked decrease in muscle activity and interactions with th ...

, and the

reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...

. The neurons send processes to a region connecting to the

pituitary stalk The pituitary stalk, also known as the infundibular stalk, infundibulum, or Fenderson's funnel, is the connection between the hypothalamus and the posterior pituitary, the posterior lobe of the pituitary gland. The floor of the third ventricle is ...

and

s are delivered into the bloodstream. They are carried by portal vessels to the pituitary cells where they may stimulate, inhibit, or maintain the function of a particular cell type.

References

External links

* * {{Cell signaling Nervous tissue cells Endocrine cells