Some of the many functions of the Liver

1) Synthesizes:Many blood protein components:

Carrier Proteins, blood clotting factors, proteins tomaintain osmotic balance, etc.

Somatomedins (Insulin-like growth factors, IGFs)

2) Serves in carbohydrate storage and metabolism, andcholesterol metabolism

3) Iron, ferritin, bilirubin metabolism – removal of “wornout” erythrocytes and recycling/elimination of Hbbyproducts/components.

4) Digestion – bile and bicarbonates

5) Breakdown or transformation of hormones, wastes(nitrogenous), drugs and toxins (as well as ketogenesis)

The Greatest Threats to your Liver

1) Drugs:

Alcoholism

Acetominophen (ordinary Tylenol) overdose

2) Food poisoning:

Deadly Amanitas

3) Hepatitis viruses

Hepatitis

Virus infection carcinogenic mode oftransmission

vaccine? comments

A (RNA) acute butself-limited no

enteric (fecal-oral)

food/waterchild daycare

yes (rec.for infants

and totravelers)

B (DNA) both acute &chronic

cirrhosisYES

serum (sex &IV drug

abuse), &transplacental

yes (rec.for pre-teens)

Human liversare futile;baboons -

goodxenotranspl.

C (RNA) Chroniccirrhosis

YES same as B NO futile

D (RNA) acute andchronic

cirrhosis

YES same as B NO

E (RNA) acute butself-limited,

but oftenlethal inpregnantwomen

enteric (mainly3rd world

countries)

NO lethal topregnant

women ??

Hepatitis C

Hep C is, because of its transmission via serum and bodyfluids, a STD:

1) estimated, approximately 4 million americans are infected (that’s about 4 times as many as have HIV)

2) 5% of those infected are predicted to develop livercancer*

3) while 15% may resist it and not show clinical effects,they are nevertheless transmitters of the virus

4) 80% of those infected, if not treated, will develop chroniccirrhosis and may progress to liver failure*

* note that infection with Hep C largely eliminates youfrom eligibility on the Liver transplant list.

The Appendix: what & why?• Convention thought is that it is a vestige of an

“active” Ceacum – used to digest cellulose in some herbivorous species. But few species show this vestigial organ.

• But a recent hypothesis by Dr. William Parker, albeit untested, is that is a derived organ that provides a refugium for beneficial, commensal microflora – to repopulate the gut if/when a pathogen/toxin flushes through the colon and wipes out the commensals.

Remember ….

Water (and the electrolytes) Conservation!!! … an important

concern of any terrestrial organism.

And diarrhea-type diseases (cholera, dysentery, etc.) kills 25 million

children in the world every year!

Initiation of the Digestive Process

Cephalic Phase: neurological (vagal n.)

Gastric Phase: in stomach …

Positive Feedback Loop:products of digestion:1) lowers muscle stimulus threshholds2) stimulates release of gastrin & enteroxyntin3) stimulates secretions of HCl & Pepsinogen…which in turn creates more products ofdigestion, which increases (1) through (3) somemore.

also, short (within the stomach) and long reflexes(from the medulla) aid in the stomach stimulation(although the latter is not necessary, as demonstratedby surgical destruction of the vagus n.).

Control of the Digestive Process

Intestinal Phase: in duodenum (and beyond) …

At first, the duodenum produces intestinal gastrin andbombesin, which continues to stimulate the stomach.But when the stomach’s tasks are complete, theENTEROGASTRIC REFLEX shuts down the stomach andinitiates the activities of the intestines, liver (includingthe gall bladder) and pancreas.

First, these all inhibit the stomach: 1) Neurological (short & long reflexes, again)2) Endocrine:

acids (from the stomach) stimulate secretinfats stimulate gastric inhibiting peptide, GIP, (and this

stimulates other cells to produce somatostatin)acids & fats (& amino acids) stimulate cholecystokinen.also, Bulbogastrone (not much known right now).

Control of the Digestive Process

Intestinal Phase: in duodenum (and beyond) …

ENTEROGASTRIC REFLEX, continued.

Second, this reflex also stimulates the intestinal processes:

Secretin:Pancreas to produce a bicarbonate buffer solution.Liver to produce both bile and bicarbonate.

Cholecystokinen:Pancreas to produce a “soup” of many enzymes.Gall bladder to contract and release bile.Enhances Secretin’s effect on the liver.Relaxes the Spincter of Oddi to open the Ampulla of Vater.

Gastric Inhibiting Peptide (GIP):Stimulates insulin secretion

Intestinal Gastrin:Stimulates intestinal motility and secretionsRelaxes the ileocecal sphincter

Control of the Digestive Process

There are also additional hormones:Enterocrinin

stimulates mucus and secretion of buffers

Motilina “messenger” peptide that stimulates peristaltic waves.

Vasoactive Intestinal Polypeptide (VIP)stimulates water and salt secretion, and buffers, of theintestines.

Substance Pexcites the smooth muscles of the digestive tract(stimulates segmentation and peristalsis).

Thus, the digestive tract continues to work, digesting yourmeal, largely autonomous of the CNS, controlled by hormonesand the local stimulation of the Enteric Nervous System.

Enzymes

Make a reminder in your notebooks to look at (for 8th ed):

Digestive Enzymes, Table 24-3 (pg 918)

Chemical Events, Figure 24-26 (pg 917)

Ion & Vitamin Absorption, Table 24-4 (pg 921)

and develop a feeling or sense of what they convey – you do NOT have to memorize these illustrations, but look for general principle or ideas, as well as any exceptions to these generalities.