BIO 202 Lymphatic System

What are the primary functions of the lymphatic system?

1. fluid recovery - return water and plasma to the blood

2. immunity - lymph nodes contain immune cells, filter pathogens in blood

3. lipid absorption - in small intesetines (lacteals)

What is lymph?

the recovered fluid

• clear, colorless fluid

• similar to plasma, but with less protein

• contains WBCs, lipids, and pathogens/impurities

• starts as extracellular fluid (interstitial fluid) drawn into lymphatic capillaries

• chemical composition varies in different places

What transports lymph?

lymphatic vessels

What is composed of aggregates of lymphocytes and macrophages that populate many organs in the body?

lymphatic tissues and organs

• defense cells are concentrated here

Lymphatic capillaries are present in nearly every tissue except:

cartilage, cornea, bone, and bone marrow

What is the capillary wall comprised of?

overlapping endothelial cells

• gaps between cells are big enough to let bacteria and other cells in

• endothelium creates valve-like flaps that open when interstitial fluid pressure is high to allow fluid to enter and close when it is low

  • pressure is highest in blood capillaries, then in interstitial space, and lowest in veins

interstitium

filled with interstitial fluid that eventually is recovered by lymphatic capillaries to become lymph

What are the six lymphatic trunks?

1. jugular

2. subclavian

3. broncho-mediastinal

4. intercostal

5. intenstinal

6. lumbar trunks

The two collecting ducts are ____ and _____ and drain lymph into the subclavian veins

• right lymphatic duct

  • drains right arm, right upper thorax, right side of head/neck into right subclavian

• thoracic duct

  • drains everything else

What is the flow of lymph?

lymphatic capillaries → collecting vessels → 6 lymphatic trunks → right lymphatic duct OR thoracic duct → subclavian veins

thoracic duct

• larger and longer than the right lymphatic duct

• originates as cisterna chyli

  • receives lymph from below the diaphragm

  • named for fatty lymph received from small intestines

What are the two primary lymphoid organs?

• bone marrow

• thymus

bone marrow

located inside bones

• produces all blood cells, WBCs, site for maturation of B cells

thymus

houses developing T lymphocytes

• bilobate organ located in mediastinum between sternum and aortic arch

• member of enodcrine AND lymphatic systems

• largest lymphatic organ through adolescence

  • degenerates with age

• secretes hormones regulating T-cell development

  • Thymosin, thymulin, thymopoietin

What is the outer connective tissue layer of the thymus?

capsule

What is the dark blue stained area of thymus that is packed with maturing T cells?

cortex

Secondary lymphoid organs

tonsils, spleen, lymph nodes

What are tonsils?

• patches of lymphatic tissue located at the entrance to the pharynx

• guards against ingested or inhaled pathogens

• covered with epithelium

tonsilar crypts

deep pits lined with lymphatic tissue

What are the 3 types of tonsils?

• pharyngeal tonsil (1)

  • known as adenoids

  • single tonsil on wall of nasopharynx

• palatine tonsils (2)

  • pair at posterior margin of oral cavity

  • most often infected

• lingual tonsils (2)

  • pair at root of tongue

spleen

• largest lymphatic organ in adults

• highly vascularized to filter blood

• 2 tissue types

  • red pulp = sinuses with erythrocytes and platelets

  • white pulp = lymphocytes, macrophages, surrounding small branches of splenic artery to initiate immune response

functions of spleen

• white pulp monitors blood for foreign antigens and keeps an army of monocytes for release

• stabilizes blood volume through plasma transfers to lymphatic system

• healthy erythrocytes come and go

• erythrocyte graveyard for old RBCs

  • old RBCs rupture in sinus capillaries

lymph nodes

• small, bean shaped glands hosting lymphocytes, macrophages (APCs)

• most numerous lymphatic organs

  • 450 in adults

• highly concentrated in cervical, axillary, thoracic, abdominal, intestinal, inguinal, and popliteal regions

2 main functions of lymph nodes

• cleanse the lymph (remove 99% of impurities)

• act as a site of T and B cell activation

What allows circulating lymphocytes to enter the lymph node?

high endothelial venule (HEV)

germinal center

contains activated B cells that are differentiating to plasma cells

lymphedema

accumulation of interstitial fluid secondary to obstructed lymphatic vessels

• elephantiasis is an example of lymphedema caused by roundworms

lymph nodes and metastatic cancer

• metastatic cencer cells can easily enter lymphatic vessels and travel to new tissue

• lodge in the 1st lymph node (sentinel node) they encounter

• trapped cells multiply and destroy the node

  • causes swelling, firmness, but usually painless

• cancerous cells typically spread to other nodes downstream

  • that’s why treatment of breast cancer = lumpectomy + removal of axillary nodes

What is the difference between endocrine and exocrine secretions?

• endocrine secretes directly into the bloodstream

• exocrine secretes via ducts (exit)

  • primarily refers to digestive secretions

paracrine

secretes chemical diffuses through the interstitial space and has affect on neighboring cells

• somatostatin secreted by pancreatic cells

autocrine

the chemical secreted has effect on the same cell that just secreted it

• an activated T-cell secretes IL-2 that comes back and binds IL-2 receptors on the same cell

humoral stimuli - blood solute concentration

some glands secrete their hormone in direct response to changing blood levels of certain critical nutrients and ions

• ex. parathyroid gland secretes PTH in response to low blood calcium levels

• high levels of glucose in the blood can cause the release of insulin

neural stimuli - autonomic nervous system

not common but a good example is sympathetic nervous system stimulation of the adrenal gland medulla to release catecholamines (norepinephrine and epinephrine)

• fight or flight

• being chased by a bear with chainsaw hands activates your sympathetic nervous system, causing release of EPI

hormonal stimuli - tropic hormones

many endocrine glands secrete their hormone in response to other endocrine glands

• Hormone A released by Organ A and acts on Organ B causing the release of Hormone B

• TSH released by the adenohypophysis causes the thyroid gland to release TH

hormones stimulate only those cells that have functioning _____ for them

receptors

• if present, hormone can bind and initiate changes in cellular metabolic activity

Where are receptors for lipid-based hormones (sterioid hormones) located?

• cytoplasm

Where are receptors for lipid-insoluble hormones (peptide hormones)?

imbedded in the plasma membrane

• these hormones cannot penetrate the cell membrane

synergistic effects

2 or more hormones work together to produce a greater effect than each can alone

• FSH and testosterone facilitate normal sperm production

permissive effects

1 hormone is required for a later hormone to exert its full effect

• estrogen prepares the uterus for the action of progesterone

antagonistic effects

2 hormones have opposing physiological actions

• insulin lowers blood glucose and glycogen increases it

How can hormone sensitivity be modulated?

altering receptor density

• up-regulation = increase in total number of receptors for increase in sensitivity

• down-regulation = decrease in total receptors for decreased sensitivity

  • occurs with long-term exponsure to high hormone concentrations

negative feedback

occurs when hormone levels reach such concentrations that the pathway to produce the target hormone is inhibited or turned off

positive feedback

occurs when a stimuli triggers the release of a hormone, which in turn strengthens the initial stimuli

• promotes release of additional hormone and further strengthens the initial stimuli

What are the 3 endocrine organs of the brain?

• hypothalamus

• pituitary gland

• pineal gland

hypothalamus

King of the endocrine system

• most endocrine functions start with input here

• links nervous and endocrine systems

• all vertebrates have one

• all of the hormones (tropic) released directly affect the pituitary gland

• maintains rich connection to the cortex, brainstem, and autonomic zones and limbic system

• ex. hunger, thirst, temperature, fatigue, sleep, reproductive and attachment behaviors

What are hormones released by the hypothalamus?

• corticotropin-releasing hormone (CRH)

• gonadotropin-releasing hormone (GnRH)

• thyrotropin-releasing hormone (TRH)

• Growth Hormone-releasing hormone (GHRH)

• Growth Hormone-Inhibiting hormone (GHIH or Somatostatin)

• Prolactin-releasing hormone (PRH)

• Prolactin-inhibiting hormone (PIH)

corticotropin-releasing hormone (CRH)

• stimuli = low cortisol levels

• origin = hypothalamus

• target = anterior pituitary gland

• action = causes release of ACTH

• inhibition = high cortisol

Gonadotropin releasing hormone (GnRH)

stimuli: low testosterone or estrogen

origin: hypothalamus

target: anterior pituitary gland

action: causes release of FSH or LH

inhibition: high testosterone or estrogen

Thyrotropin-releasing hormone (TRH)

stimuli: low thyroid hormone levels

origin: hypothalamus

target: anterior pituitary gland

action: cases release of TSH

inhibition: high thyroid hormone levels

Growth hormone releasing hormone (GHRH)

stimuli: deep sleep, puberty, intense exercise, low levels of GH

origin: hypothalmus

target: anterior pituitary gland

action: causes release of GH

inhibition: old age, high levels of cortisol, high levels of GH

Growth Hormone Inhibiting Hormone (GHIH) or Somatostatin

stimuli: very high levels of GH, high calcium or glucose levels

origin: hypothalamus

target: anterior pituitary gland

action: inhibits release of GH

inhibition: low levels of GH, exercise, deep sleep

Prolactin releasing hormone (PRH)

stimuli: low milk reserves, sexual gratification

origin: hypothalamus

target: anterior pituitary gland

action: causes release of PRH

inhibition: high milk reserves, arousal

prolactin inhibiting hormone (PIH)

stimuli: high milk reserves, sexual arousal

origin: hypothalamus

target: anterior pituitary gland

action: inhibits release of prolactin

inhibition: low milk reserves, sexual gratification

pituitary gland

• most hormones from this gland help maintain homeostasis

• also known as the hypophysis

  • rests in the hypophyseal fossa of the sella turcica of the sphenoid bone

• divided into 2 distinct regions

anterior pituitary or adenohypophysis

• synthesizes and releases hormones

• release is controlled by hypothalamus

• originates from oral ectoderm; not nervous tissues

posterior pituitary or neurohypophysis

• stores hormones produced in the hypothalamus and releases them

• originate from neural ectoderm

Match the hypothalamic hormone to the anterior pituitary gland hormone it stimulates: corticotropin-releasing hormone (CRH)

adenocorticotropic hormone (ACTH)

• adrenal gland release glucocorticoids

Match the hypothalamic hormone to the anterior pituitary gland hormone it stimulates: gonadotropin-releasing hormone (GnRH)

• follicle-stimulating hormone (FSH)

• lutenizing hormone (LH)

Match the hypothalamic hormone to the anterior pituitary gland hormone it stimulates: thyrotropin-releasing hormone (TRH)

thyroid-stimulating hormone (TSH) or thyrotropin

Match the hypothalamic hormone to the anterior pituitary gland hormone it stimulates: growth hormone-releasing hormone (GHRH)

growth hormone

Match the hypothalamic hormone to the anterior pituitary gland hormone it inhibits: growth hormone-inhibiting hormone (GHIH) or somatostatin

growth hormone

Match the hypothalamic hormone to the anterior pituitary gland hormone it inhibits: prolactin-inhibiting hormone (PIH)

prolactin (PRL)

anterior pituitary hormones

• adrenocorticotropic hormone (ACTH)

• follicle-stimulating hormone (FSH)

• lutenizing hormone (LH)

• thyroid-stimulating hormone (TSH)

• growth hormone (GH)

• prolactin (PRL)

neurohypophysis

• antidiuretic hormone (ADH) or vasopressin

• oxytocin (OT)

adrenocorticotropic hormone (ACTH)

stimuli: high levels of CRH

secreted from: anterior pituitary gland

target: adrenal cortex

action: release of cortisol

inhibition: low levels of CRH

follicle-stimulating hormone (FSH)

stimuli: high levels of GnRH

secreted from: anterior pituitary gland

target: testes or ovaries

action: stimulates egg development or sperm production

inhibition: low levels of GnRH, high levels of inhibin

lutenizing hormone (LH)

stimuli: high levels of GnRH

secreted from: anterior pituitary gland

target: testes or ovaries

action: release of testosterone or estrogen

inhibition: low levels of GnRH

thyroid-stimulating hormone (TSH)

stimuli: high levels of TRH

secreted from: anterior pituitary gland

target: thyroid

action: release of TH

inhibition: low levels of TRH

growth hormone (GH)

stimuli: high levels of GHRH, low levels of GHIH

secreted from: anterior pituitary gland

target: liver and muscles

action: increase use of fats, muscle uptake of glucose, bone, muscle and cartilage cell growth

inhibition: high levels of GHIH, low levels of GHRH

prolactin (PRL)

stimuli: high levels of PRH, low levels of PIH

secreted from: anterior pituitary gland

target: mammary glands, testes

action: causes milk production, stimulates LH secretion

inhibition: low levels of PRH, high levels of PIH

metabolic actions of growth hormone

1. hypothalamus secretes growth hormone-releasing hormone (GHRH) and somatostatin (GHIH)

2. Liver and other tissues effected / anti-insulin actions

3. Insulin-like growth factors / anti-insulin actions

4. Skeletal effects, extraskeletal effects / fat, carbohydrate metabolism

5. increased cartilage formation and skeletal growth, increased protein synthesis and cell growth / increased lipolysis, increased blood glucose and other anti-insulin effects

oxytocin

stimuli: uterine stretching, suckling, sex/romance

secreted from: posterior pituitary gland (made in hypothalamus)

target: uterus, mammary glands, memory center

action: stronger uterine contractions, causes milk ejection, bonding

inhibition: uterine wall stops stretching, no suckling, bad history

antidiuretic hormone (ADH)

stimuli: low blood pressure or reduced plasma volume (high osmolarity)

secreted from: posterior pituitary gland, made in hypothalamus

target: kidneys

action: causes retention of water/increased water reabsorpbtion in kidneys, moderate vasoconstriction and increase of blood pressure

inhibition: high plasma volume, high blood pressure, alcohol or caffeine

pineal gland/body

• believed to help coordinate physiological processes with 24-hour circadian rhythms

• produces 2 hormones:

  • melatonin - sleepy hormone

  • serotonin - happy hormone

melatonin

stimuli: decreased light or night

secreted from: pineal gland/body

target: brain

action: believed to cause sleepiness, may help sync physiological processes to circadian rhythms

inhibition: bright light (sunlight), high serotonin levels

serotonin

stimuli: bright light (sunlight)

secreted from: prineal gland/body

target: brain

action: believed to cause alertness and happiness

inhibition: decreased light or night