Gallbladder Anatomy

Located in the RUQ, the gallbladder is a small organ that aids in digestion.  It secretes bile into the cystic duct where it is joined by the common hepatic duct and forms the common bile duct which empties into the duodenum when fat is being digested.  The gallbladder consists of three parts: the fundus, body and neck. It is supplied by the cystic artery. It is innervated by the vagus nerve and celiac ganglia.

Medulla

The medulla is the inferior part of the brain stem. 

The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and deals with autonomic functions such as breathing, heart rate and BP.

 

It contains:

1) nuclei (neurons) of the cranial nerves:

• IX = salivation
• X = PS efferent supply of thoracic & abdominal viscera (heart, lung, GI)

2) Reticular formation- a diffuse group of brainstem nuclei that modulate activity of the nervous system by filtering incoming stimuli and ignoring the irrelevant background stimuli.

3) Area postrema– vomiting center. Has no protection from the blood brain barrier.

Limbic System

The limbic system is involved in the generation of emotions, instincts and memories.  It receives instructions from the hypothalamus and projects instructions to the areas of the cerebral cortex responsible for cognition and intelligent decisions. The response from these cortex areas is sent back to the limbic system, hypothalamus and reticular formation, changing the activity of the descending autonomic efferent pathways and secreting pituitary hormones.

Hypothalamus

The hypothalamus is the major autonomic regulatory center. It’s main function is to regulate homeostasis through:

• water balance
• temperature
• feeding

It receives sensory info (osmo, baro, visual receptors etc) from many autonomic afferent fibers such as the vagus nerve and glossopharingeal nerve. The information is collected and sorted and an endocrine response is elicited. The info is then sent to the amygdala and other structures of the limbic system where a behavior response is elicited.

Somatic Nervous System

The somatic nervous system is an efferent nervous system. Controls voluntary movement of body parts.

Transmitter: Ach (NMJ)

Pathway: 1 neuron (1 ax0n) pathway from CNS

Nerve fibers: Large (type A, large myellinated)

ANS

The ANS is an efferent nervous system which is based on involuntary controls. 

Transmitters: ACH, NE or peptide cotransmitters

Pathway:  1. preganglionic (type B myelinated fibers) & postganglionic (type C unmyellinated) neurons

Nerve fibers: small

Efferent Autonomic Reflexes of Cranial Nerves

Efferent autonomic reflexes carry impulses from the CNS to the viscera via the autonomic system.

Vagal nerve (CN X) – decreases heart rate.  Can be triggered by either somatic or visceral sensory afferents.

Trigemino-vagal – oculocardiac and diving = pulse drop in response to pressure applied to eye or stimulation of facial skin.

Nerve Fibers of the PNS

Afferent – sensory nerve fibers bring impulses to the CNS = receptors.

Efferent– motor nerve fibers bring impulses to the periphery = skeletal muscles, smooth muscle, cardiac muscle, gland.

Peripheral Nervous System

Consists of 12 pairs of cranial nerves.

31 pairs of spinals nerves plus ganglia and receptor cells.

Attached to each segment of the spinal cord is a pair of spinal nerves that are attached by ventral and dorsal roots.

The dorsal roots contain sensory axons and their neurons are in the dorsal root ganglion.

The ventral roots contain motor axons that come from cell bodies in the gray matter.

Each spinal nerve is a mix of sensory and motor fibers.

Vessel Types

ELASTIC ARTERIES

• large arteries, aorta
• conduct flow w/ little energy loss
• distensible due to large elastic component of wall
• transiently store blood during ventricular ejection
• recoil during ventricular relaxation
• maintain flow to peripheral arteries

MUSCULAR ARTERIES

• small arteries
• bring blood to organs
• minor factor in TPR

ARTERIOLES

• regulate flow by changing D
• major factor in TPR

TERMINAL ARTERIOLES

• pre-capillary spinchters
• fine tuning for capillary network pressure, flow and exchange

CAPILLARIES

• blood-tissue exchange
• diameter doesn’t change
• endothelial cells of capillaries release vasoactive substances, control diameter

VENULES/VEINS

• thin walled but have some VSM
• store/mobilize blood volume